Changed Reminder Systematics analogue to invoices

Move the invoice draft editor to a backend single source of truth: an
in-memory InvoiceDraftSession (per-token, cached) holds the editable payload,
server-computed sums/VAT and validation, plus an automatic change history. The
browser posts single edits; the server recomputes and signals the editing
session over a dedicated SignalR hub (DraftPreviewHub) to re-fetch.

This reverses the previously-documented stateless editor (EVAL_live_invoice_editing,
INVOICE_LIFECYCLE §10), by explicit product decision — captured in ADR 0006 and 0007
plus the live-draft-editing concept doc.

Backend (this milestone):
- InvoiceDraftSession + ChangeHistoryEntry data holders
- InvoiceDraftCalculator: pure port of quantChange/invSumUpdate (§13b, VAT-by-rate)
  and consistency checks — fully unit-tested
- IInvoiceDraftCache/InvoiceDraftCache: in-memory store with idle sliding TTL
- IInvoiceDraftService/InvoiceDraftEditService: open (payload or DB reload), patch,
  build state, flush via existing RegisterInvoiceAsync (no new persistence), preview
  from cache, discard (DB reload), history
- InvoiceDraftExpiryService: pre-expiry warning + eviction-with-reason
- DraftPreviewHub + IDraftNotifier/DraftNotifier: targeted draftReady/draftExpiring/
  draftClosed signals per draft token
- inv/dopen|dstate|dpatch|dpreview|dsave|dhistory|ddiscard|dclose endpoints; save
  reports success/failure via the existing EventService
- DI + hub mapping in Program.cs

Frontend (additive foundation): $fis.draft SignalR client for /draftpreview.
The editor DOM inversion (routing deltas, rendering from server state) is the
next, separately-verified step; existing endpoints are unaffected.

Tests: 30 new (calculator, cache, expiry, patch/history, flush); 306 total passing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Fuchs.Tests/FdsInvoiceDataBlocksTests.cs

@@ -0,0 +1,52 @@
+using System.Linq;
+using Fuchs.intranet;
+using Newtonsoft.Json.Linq;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Verifies the block projection that feeds the PDF item table: each service-request
+/// group exposes its heading (the section title the editor shows) and its line items,
+/// so the PDF can print a heading row per block and the flat item list still works.
+/// </summary>
+public class FdsInvoiceDataBlocksTests
+{
+    private static FdsInvoiceData FromReq(string reqJson) =>
+        new(JObject.Parse(@"{'admin':{'type':'r'},'new':{},'sms':{},'req':" + reqJson + "}"));
+
+    [Fact]
+    public void InvoiceBlocks_ExposesHeadingFromTextThenNme_AndItems()
+    {
+        var inv = FromReq(@"[
+          {'Id':'1','text':'Sektion A','items':[{'id':'a','type':'material','title':'X','price_net':10,'total_net':10}]},
+          {'Id':'2','nme':'Sektion B','items':[{'id':'b','type':'material','title':'Y','price_net':20,'total_net':20}]}
+        ]");
+
+        var blocks = inv.InvoiceBlocks;
+
+        Assert.Equal(2, blocks.Count);
+        Assert.Equal("Sektion A", blocks[0].Heading);
+        Assert.Equal("Sektion B", blocks[1].Heading);      // falls back to nme
+        Assert.Single(blocks[0].Items);
+        Assert.Equal("X", blocks[0].Items[0]["title"]);
+    }
+
+    [Fact]
+    public void InvoiceBlocks_MissingHeading_IsEmpty()
+    {
+        var inv = FromReq(@"[{'Id':'1','items':[{'id':'a','type':'material','total_net':5}]}]");
+        Assert.Equal("", Assert.Single(inv.InvoiceBlocks).Heading);
+    }
+
+    [Fact]
+    public void InvoiceItems_StillFlattensAcrossBlocks()
+    {
+        var inv = FromReq(@"[
+          {'Id':'1','text':'A','items':[{'id':'a','type':'material','total_net':10}]},
+          {'Id':'2','text':'B','items':[{'id':'b','type':'material','total_net':20},{'id':'c','type':'material','total_net':30}]}
+        ]");
+
+        Assert.Equal(new[] { "a", "b", "c" }, inv.InvoiceItems.Select(i => i["id"]!.ToString()).ToArray());
+    }
+}

Fuchs.Tests/InvoiceDraftCacheTests.cs

@@ -0,0 +1,113 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Fuchs.intranet;
+using Fuchs.Notifications;
+using Fuchs.Services;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Covers the in-memory draft cache (storage + idle sliding TTL) and the background
+/// expiry monitor that warns before eviction and closes the editor on eviction (ADR 0006).
+/// </summary>
+public class InvoiceDraftCacheTests
+{
+    private static IConfiguration Config(int idle = 30, int warn = 5) =>
+        new ConfigurationBuilder().AddInMemoryCollection(new Dictionary<string, string?>
+        {
+            ["Fuchs:DraftEditing:IdleMinutes"] = idle.ToString(),
+            ["Fuchs:DraftEditing:ExpiryWarnMinutes"] = warn.ToString()
+        }).Build();
+
+    private sealed class FakeNotifier : IDraftNotifier
+    {
+        public readonly List<(string token, int version)> Ready = new();
+        public readonly List<(string token, int secondsLeft)> Expiring = new();
+        public readonly List<(string token, string reason)> Closed = new();
+        public Task SignalDraftReadyAsync(string token, int version, CancellationToken ct = default) { Ready.Add((token, version)); return Task.CompletedTask; }
+        public Task SignalExpiringAsync(string token, int secondsLeft, CancellationToken ct = default) { Expiring.Add((token, secondsLeft)); return Task.CompletedTask; }
+        public Task SignalClosedAsync(string token, string reason, CancellationToken ct = default) { Closed.Add((token, reason)); return Task.CompletedTask; }
+    }
+
+    // ── Cache storage ─────────────────────────────────────────────────────────
+    [Fact]
+    public void SetGet_RoundTrips_AndUnknownTokenIsNull()
+    {
+        var cache = new InvoiceDraftCache(Config());
+        var s = new InvoiceDraftSession { Token = "abc" };
+        cache.Set(s);
+        Assert.Same(s, cache.Get("abc"));
+        Assert.Null(cache.Get("nope"));
+    }
+
+    [Fact]
+    public void Remove_EvictsSession()
+    {
+        var cache = new InvoiceDraftCache(Config());
+        cache.Set(new InvoiceDraftSession { Token = "x" });
+        Assert.NotNull(cache.Remove("x"));
+        Assert.Null(cache.Get("x"));
+        Assert.Null(cache.Remove("x"));
+    }
+
+    [Fact]
+    public void Get_ResetsExpiryWarningFlag_SoAFreshWarningIsDue()
+    {
+        var cache = new InvoiceDraftCache(Config());
+        var s = new InvoiceDraftSession { Token = "x", ExpiryWarningSent = true };
+        cache.Set(s);
+        cache.Get("x");
+        Assert.False(s.ExpiryWarningSent);
+    }
+
+    // ── Expiry monitor ────────────────────────────────────────────────────────
+    [Fact]
+    public async Task Sweep_NearTtl_WarnsOnceThenEvictsWithReason()
+    {
+        var cfg = Config(idle: 30, warn: 5);
+        var cache = new InvoiceDraftCache(cfg);
+        var notifier = new FakeNotifier();
+        var svc = new InvoiceDraftExpiryService(cache, notifier, cfg, NullLogger<InvoiceDraftExpiryService>.Instance);
+
+        var s = new InvoiceDraftSession { Token = "a" };
+        cache.Set(s);
+
+        // Idle 26 min → inside the 5-min warning window (30-5=25) but not yet expired.
+        s.LastAccessUtc = DateTime.UtcNow.AddMinutes(-26);
+        await svc.SweepAsync(CancellationToken.None);
+        Assert.Single(notifier.Expiring);
+        Assert.Empty(notifier.Closed);
+        Assert.True(s.ExpiryWarningSent);
+
+        // Another sweep while still idle must not spam a second warning.
+        await svc.SweepAsync(CancellationToken.None);
+        Assert.Single(notifier.Expiring);
+
+        // Past the TTL → evicted and the editor is told to close with a reason.
+        s.LastAccessUtc = DateTime.UtcNow.AddMinutes(-31);
+        await svc.SweepAsync(CancellationToken.None);
+        Assert.Single(notifier.Closed);
+        Assert.Equal(("a", "expired"), notifier.Closed[0]);
+        Assert.Null(cache.Get("a"));
+    }
+
+    [Fact]
+    public async Task Sweep_FreshSession_DoesNothing()
+    {
+        var cfg = Config(idle: 30, warn: 5);
+        var cache = new InvoiceDraftCache(cfg);
+        var notifier = new FakeNotifier();
+        var svc = new InvoiceDraftExpiryService(cache, notifier, cfg, NullLogger<InvoiceDraftExpiryService>.Instance);
+        cache.Set(new InvoiceDraftSession { Token = "fresh" });
+
+        await svc.SweepAsync(CancellationToken.None);
+
+        Assert.Empty(notifier.Expiring);
+        Assert.Empty(notifier.Closed);
+    }
+}

Fuchs.Tests/InvoiceDraftCalculatorTests.cs

@@ -0,0 +1,212 @@
+using Fuchs.intranet;
+using Newtonsoft.Json.Linq;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Verifies the server-side aggregation of invoice draft totals (the port of the
+/// former client-side <c>invSumUpdate</c> footer math). The truth now lives in the
+/// backend (ADR 0006), so this is unit-testable directly. Line values are read from
+/// each block's <c>itm</c> array (the editor's <c>co</c> objects: <c>vt</c>=net,
+/// <c>vv</c>=VAT, <c>vs</c>=service-net, <c>vsv</c>=service-VAT, <c>vat</c>=rate).
+/// </summary>
+public class InvoiceDraftCalculatorTests
+{
+    private static InvoiceDraftSession SessionWith(string reqJson, bool p13b = false)
+    {
+        var s = new InvoiceDraftSession { Token = "t" };
+        s.Admin = new JObject { ["p13b"] = p13b };
+        s.New = new JObject { ["invoiceemail"] = "kunde@example.de", ["invoiceaddress"] = "Weg 1" };
+        s.Req = JArray.Parse(reqJson);
+        return s;
+    }
+
+    [Fact]
+    public void RecomputeTotals_SumsNetVatServiceAndPerBlock()
+    {
+        var s = SessionWith(@"[
+          { 'Id':'10','itm':[
+             {'vt':100,'vv':19,'vs':0,'vsv':0,'vat':'19%'},
+             {'vt':50,'vv':9.5,'vs':50,'vsv':9.5,'vat':'19%'} ] },
+          { 'Id':'11','itm':[
+             {'vt':200,'vv':14,'vs':0,'vsv':0,'vat':'7%'} ] }
+        ]");
+
+        InvoiceDraftCalculator.RecomputeTotals(s);
+
+        Assert.Equal(350m, s.Sums.TotalNet);
+        Assert.Equal(42.5m, s.Sums.TotalVat);
+        Assert.Equal(392.5m, s.Sums.TotalGross);
+        Assert.Equal(50m, s.Sums.ServiceNet);
+        Assert.Equal(9.5m, s.Sums.ServiceVat);
+        Assert.Equal(28.5m, s.Sums.VatByRate["19"]);
+        Assert.Equal(14m, s.Sums.VatByRate["7"]);
+        Assert.Equal(150m, s.Sums.NetByBlock["10"]);
+        Assert.Equal(200m, s.Sums.NetByBlock["11"]);
+    }
+
+    [Fact]
+    public void RecomputeTotals_ReverseCharge_SuppressesVatAndGrossEqualsNet()
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[ {'vt':100,'vv':19,'vat':'19%'} ] }]", p13b: true);
+
+        InvoiceDraftCalculator.RecomputeTotals(s);
+
+        Assert.Equal(100m, s.Sums.TotalNet);
+        Assert.Equal(100m, s.Sums.TotalGross);
+        Assert.Equal(0m, s.Sums.TotalVat);
+        Assert.Empty(s.Sums.VatByRate);
+    }
+
+    [Fact]
+    public void RecomputeTotals_EmptyDraft_AllZero()
+    {
+        var s = SessionWith("[]");
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        Assert.Equal(0m, s.Sums.TotalNet);
+        Assert.Equal(0m, s.Sums.TotalGross);
+        Assert.Empty(s.Sums.VatByRate);
+    }
+
+    [Theory]
+    [InlineData("19,0%", "19")]
+    [InlineData("7%", "7")]
+    [InlineData("19", "19")]
+    [InlineData("", "")]
+    [InlineData("0", "")]
+    [InlineData("7,5", "7.5")]
+    public void NormalizeRate_CanonicalisesRateStrings(string raw, string expected)
+        => Assert.Equal(expected, InvoiceDraftCalculator.NormalizeRate(raw));
+
+    [Fact]
+    public void Validate_ValidDraft_NoErrors()
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[ {'vt':100,'vv':19,'vat':'19%'} ] }]");
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.DoesNotContain(s.ValidationMessages, m => m.Severity == "error");
+    }
+
+    [Theory]
+    [InlineData("", "warning")]
+    [InlineData("not-an-email", "error")]
+    public void Validate_EmailProblems_AreFlagged(string email, string severity)
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[{'vt':10,'vat':'19%'}] }]");
+        s.New["invoiceemail"] = email;
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "email" && m.Severity == severity);
+    }
+
+    [Fact]
+    public void Validate_NoItems_IsError()
+    {
+        var s = SessionWith("[]");
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "items" && m.Severity == "error");
+    }
+
+    [Fact]
+    public void Validate_UnknownVatRate_IsWarning()
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[{'vt':10,'vv':0.5,'vat':'5%'}] }]");
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "vat" && m.Severity == "warning");
+    }
+
+    [Fact]
+    public void Validate_MissingAddress_IsWarning()
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[{'vt':10,'vat':'19%'}] }]");
+        s.New["invoiceaddress"] = "";
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "address" && m.Severity == "warning");
+    }
+
+    [Fact]
+    public void Validate_NegativeTotal_IsWarning()
+    {
+        var s = SessionWith(@"[{ 'Id':'1','itm':[{'vt':-50,'vv':0,'vat':''}] }]");
+        InvoiceDraftCalculator.RecomputeTotals(s);
+        InvoiceDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "total" && m.Severity == "warning");
+    }
+
+    // ── RecomputePositions ────────────────────────────────────────────────────
+    private static string Pos(InvoiceDraftSession s, int block, int line) =>
+        ((JObject)((JArray)((JObject)s.Req[block])["itm"]!)[line])["p"]!.ToString();
+
+    [Fact]
+    public void RecomputePositions_NumbersPricedLinesContinuouslyAcrossBlocks()
+    {
+        var s = SessionWith(@"[
+          { 'Id':'10','itm':[ {'id':'a','typ':'material','vt':1}, {'id':'b','typ':'service','vt':2} ] },
+          { 'Id':'11','itm':[ {'id':'c','typ':'material','vt':3} ] }
+        ]");
+
+        InvoiceDraftCalculator.RecomputePositions(s);
+
+        Assert.Equal("1", Pos(s, 0, 0));
+        Assert.Equal("2", Pos(s, 0, 1));
+        Assert.Equal("3", Pos(s, 1, 0));   // continuous, not restarting per block
+    }
+
+    [Fact]
+    public void RecomputePositions_SkipsHeadingAndFreeTextLines()
+    {
+        var s = SessionWith(@"[
+          { 'Id':'10','itm':[
+             {'id':'t','typ':'Title','vt':0},
+             {'id':'a','typ':'material','vt':1},
+             {'id':'x','typ':'Text','vt':0},
+             {'id':'b','typ':'material','vt':2} ] }
+        ]");
+
+        InvoiceDraftCalculator.RecomputePositions(s);
+
+        Assert.Equal("", Pos(s, 0, 0));    // title carries no number
+        Assert.Equal("1", Pos(s, 0, 1));
+        Assert.Equal("", Pos(s, 0, 2));    // free text carries no number
+        Assert.Equal("2", Pos(s, 0, 3));
+    }
+
+    [Fact]
+    public void RecomputePositions_NumbersSetHeaderLikeAnyItem()
+    {
+        // A set header is numbered just like the editor numbers it — only text/title lines are skipped.
+        var s = SessionWith(@"[
+          { 'Id':'10','itm':[
+             {'id':'h','typ':'set','vt':1000},
+             {'id':'a','typ':'material','vt':600},
+             {'id':'b','typ':'material','vt':400} ] }
+        ]");
+
+        InvoiceDraftCalculator.RecomputePositions(s);
+
+        Assert.Equal("1", Pos(s, 0, 0));   // set header keeps position 1 (matches the editor)
+        Assert.Equal("2", Pos(s, 0, 1));
+        Assert.Equal("3", Pos(s, 0, 2));
+    }
+
+    [Fact]
+    public void RecomputePositions_AfterBlockOrderChange_RenumbersToNewSequence()
+    {
+        var s = SessionWith(@"[
+          { 'Id':'10','itm':[ {'id':'a','typ':'material','vt':1} ] },
+          { 'Id':'11','itm':[ {'id':'b','typ':'material','vt':2} ] }
+        ]");
+        // Simulate a section reorder: swap the two blocks.
+        var b0 = s.Req[0]; var b1 = s.Req[1];
+        s.Req = new JArray(b1.DeepClone(), b0.DeepClone());
+
+        InvoiceDraftCalculator.RecomputePositions(s);
+
+        Assert.Equal("1", Pos(s, 0, 0));   // formerly block 11's item is now position 1
+        Assert.Equal("2", Pos(s, 1, 0));
+    }
+}

Fuchs.Tests/InvoiceDraftNotifierTests.cs

@@ -0,0 +1,126 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Fuchs.Notifications;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging.Abstractions;
+using Newtonsoft.Json.Linq;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Verifies <see cref="DraftNotifier"/> targets the draft's SignalR group (keyed by
+/// session token, ADR 0007) with the right method/payload, and — like the other
+/// notification path — swallows hub failures so a missed coordination ping never
+/// fails the underlying operation.
+/// </summary>
+public class InvoiceDraftNotifierTests
+{
+    private sealed class CapturingClientProxy : IClientProxy
+    {
+        private readonly bool _throw;
+        public string? Method { get; private set; }
+        public object?[]? Args { get; private set; }
+        public CapturingClientProxy(bool doThrow = false) => _throw = doThrow;
+        public Task SendCoreAsync(string method, object?[] args, CancellationToken cancellationToken = default)
+        {
+            if (_throw) throw new InvalidOperationException("hub down");
+            Method = method;
+            Args = args;
+            return Task.CompletedTask;
+        }
+    }
+
+    private sealed class StubHubClients : IHubClients
+    {
+        private readonly IClientProxy _proxy;
+        public string? RequestedGroup { get; private set; }
+        public StubHubClients(IClientProxy proxy) => _proxy = proxy;
+        public IClientProxy Group(string groupName) { RequestedGroup = groupName; return _proxy; }
+        public IClientProxy All => throw new NotImplementedException();
+        public IClientProxy AllExcept(IReadOnlyList<string> e) => throw new NotImplementedException();
+        public IClientProxy Client(string c) => throw new NotImplementedException();
+        public IClientProxy Clients(IReadOnlyList<string> c) => throw new NotImplementedException();
+        public IClientProxy Groups(IReadOnlyList<string> g) => throw new NotImplementedException();
+        public IClientProxy GroupExcept(string g, IReadOnlyList<string> e) => throw new NotImplementedException();
+        public IClientProxy User(string u) => throw new NotImplementedException();
+        public IClientProxy Users(IReadOnlyList<string> u) => throw new NotImplementedException();
+    }
+
+    private sealed class StubHubContext : IHubContext<DraftPreviewHub>
+    {
+        public StubHubContext(IHubClients clients) => Clients = clients;
+        public IHubClients Clients { get; }
+        public IGroupManager Groups => throw new NotImplementedException();
+    }
+
+    private static (DraftNotifier notifier, StubHubClients clients, CapturingClientProxy proxy) Create(bool doThrow = false)
+    {
+        var proxy = new CapturingClientProxy(doThrow);
+        var clients = new StubHubClients(proxy);
+        var notifier = new DraftNotifier(new StubHubContext(clients), NullLogger<DraftNotifier>.Instance);
+        return (notifier, clients, proxy);
+    }
+
+    [Fact]
+    public async Task SignalDraftReadyAsync_SendsToTokenGroupWithVersion()
+    {
+        var (notifier, clients, proxy) = Create();
+
+        await notifier.SignalDraftReadyAsync("tok-1", 7);
+
+        Assert.Equal("tok-1", clients.RequestedGroup);
+        Assert.Equal("draftReady", proxy.Method);
+        var payload = JObject.FromObject(proxy.Args![0]!);
+        Assert.Equal("tok-1", payload["token"]!.Value<string>());
+        Assert.Equal(7, payload["version"]!.Value<int>());
+    }
+
+    [Fact]
+    public async Task SignalExpiringAsync_SendsSecondsLeft()
+    {
+        var (notifier, _, proxy) = Create();
+
+        await notifier.SignalExpiringAsync("tok-2", 120);
+
+        Assert.Equal("draftExpiring", proxy.Method);
+        var payload = JObject.FromObject(proxy.Args![0]!);
+        Assert.Equal(120, payload["secondsLeft"]!.Value<int>());
+    }
+
+    [Fact]
+    public async Task SignalClosedAsync_SendsReason()
+    {
+        var (notifier, _, proxy) = Create();
+
+        await notifier.SignalClosedAsync("tok-3", "expired");
+
+        Assert.Equal("draftClosed", proxy.Method);
+        var payload = JObject.FromObject(proxy.Args![0]!);
+        Assert.Equal("expired", payload["reason"]!.Value<string>());
+    }
+
+    [Fact]
+    public async Task EmptyToken_DoesNotSend()
+    {
+        var (notifier, clients, proxy) = Create();
+
+        await notifier.SignalDraftReadyAsync("", 1);
+
+        Assert.Null(clients.RequestedGroup);
+        Assert.Null(proxy.Method);
+    }
+
+    [Fact]
+    public async Task HubFailure_IsSwallowed()
+    {
+        var (notifier, _, _) = Create(doThrow: true);
+
+        // Must not throw — a failed coordination ping cannot fail the caller's operation.
+        await notifier.SignalDraftReadyAsync("tok", 1);
+        await notifier.SignalExpiringAsync("tok", 60);
+        await notifier.SignalClosedAsync("tok", "expired");
+    }
+}

Fuchs.Tests/InvoiceDraftServiceTests.cs

@@ -0,0 +1,479 @@
+using System.Linq;
+using System.Threading.Tasks;
+using Fuchs.intranet;
+using Fuchs.Services;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+using Xunit;
+using static OCORE.OCORE_dictionaries;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Exercises the draft edit orchestrator's pure paths (open/patch/history/flush)
+/// without a database, proving the backend-authoritative model behaves correctly at
+/// the service seam (ADR 0006). Blocks use the editor's <c>itm</c>/<c>items</c> shape.
+/// </summary>
+public class InvoiceDraftServiceTests
+{
+    /// <summary>Captures the invoice handed to registration and returns it with a fake DB id — no SQL.</summary>
+    private sealed class FakeInvoiceService : IInvoiceService
+    {
+        public FdsInvoiceData? Registered;
+        public bool? LastChange;
+        public Task<FdsInvoiceData> RegisterInvoiceAsync(FdsInvoiceData invoice, bool change, string invId, string userAccountId, DatabaseSecurity dbSec)
+        {
+            Registered = invoice;
+            LastChange = change;
+            invoice.InvoiceRegistration = new GenericObjectDictionary(new System.Collections.Generic.Dictionary<string, object> { ["Id"] = "INV42" });
+            return Task.FromResult(invoice);
+        }
+        public FdsInvoiceData? PreviewInvoice;
+        public bool? PreviewDraft;
+        public Task<FdsInvoiceData> LoadInvoiceAsync(string id, string u, DatabaseSecurity s) => throw new System.NotSupportedException();
+        public Document GenerateInvoicePdf(FdsInvoiceData i, bool d) { PreviewInvoice = i; PreviewDraft = d; return new Document(); }
+        public Task<byte[]> RenderInvoicePdfBytesAsync(FdsInvoiceData i, bool d) => throw new System.NotSupportedException();
+        public Task<byte[]> StoreInvoiceDocumentFileAsync(FdsInvoiceData i, bool d, string u, DatabaseSecurity s) => throw new System.NotSupportedException();
+        public Task<byte[]?> GetInvoiceFileAsync(FdsInvoiceData i, bool d, fds.IFdsMfr m) => throw new System.NotSupportedException();
+    }
+
+    private static (InvoiceDraftEditService svc, FakeInvoiceService inv, InvoiceDraftCache cache) NewService()
+    {
+        var cache = new InvoiceDraftCache(new ConfigurationBuilder().Build());
+        var inv = new FakeInvoiceService();
+        var svc = new InvoiceDraftEditService(cache, inv, NullLogger<InvoiceDraftEditService>.Instance);
+        return (svc, inv, cache);
+    }
+
+    private static JObject Payload() => JObject.Parse(@"{
+        'admin':{'p13b':false,'type':'r','paymentterms':'10wd'},
+        'new':{'invoiceemail':'a@b.de','invoiceaddress':'Weg 1','invoicetitle':'Rechnung'},
+        'req':[{'Id':'1','text':'Auftrag','itm':[{'id':'900','typ':'material','vt':100,'vv':19,'vs':0,'vsv':0,'vat':'19%'}],
+                'items':[{'id':'900','type':'material','total_net':100,'vat':'19%'}]}]
+    }");
+
+    [Fact]
+    public void OpenFromPayload_SeedsSessionAndComputesTotals()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+        Assert.False(string.IsNullOrEmpty(s.Token));
+        Assert.Equal(0, s.Version);
+        Assert.Equal(100m, s.Sums.TotalNet);
+        Assert.Equal(119m, s.Sums.TotalGross);
+    }
+
+    [Fact]
+    public void ApplyPatch_Email_MutatesBumpsVersionAndRecordsHistory()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "email", Value = JToken.FromObject("neu@x.de") });
+
+        Assert.NotNull(s2);
+        Assert.Equal(1, s2!.Version);
+        Assert.Equal("neu@x.de", s2.New["invoiceemail"]!.Value<string>());
+        var h = Assert.Single(s2.History);
+        Assert.Equal("email", h.Target);
+        Assert.Equal("a@b.de", h.OldValue);
+        Assert.Equal("neu@x.de", h.NewValue);
+        Assert.Equal(1, h.Version);
+    }
+
+    [Fact]
+    public void ApplyPatch_BlockReplace_RecomputesTotals()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var newBlock = JObject.Parse(@"{'Id':'1','text':'Auftrag','itm':[{'id':'900','typ':'material','vt':50,'vv':9.5,'vat':'19%'}],
+                                        'items':[{'id':'900','type':'material','total_net':50,'vat':'19%'}]}");
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.replace", Ref = "1", Value = newBlock });
+
+        Assert.Equal(50m, s2!.Sums.TotalNet);
+        Assert.Equal(9.5m, s2.Sums.VatByRate["19"]);
+    }
+
+    [Fact]
+    public void ApplyPatch_BlockRemove_EmptiesDraftAndFlagsNoItems()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.remove", Ref = "1" });
+
+        Assert.Equal(0m, s2!.Sums.TotalNet);
+        Assert.Contains(s2.ValidationMessages, m => m.Field == "items" && m.Severity == "error");
+    }
+
+    [Fact]
+    public void ApplyPatch_P13bToggle_FlipsAndSuppressesVat()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "p13b" }); // no value → toggle
+
+        Assert.Equal(100m, s2!.Sums.TotalGross); // reverse-charge → gross == net
+        Assert.Empty(s2.Sums.VatByRate);
+    }
+
+    [Fact]
+    public void ApplyPatch_UnknownToken_ReturnsNull()
+    {
+        var (svc, _, _) = NewService();
+        Assert.Null(svc.ApplyPatch("ghost", new InvoiceDraftDelta { Target = "email", Value = JToken.FromObject("x@y.de") }));
+    }
+
+    [Fact]
+    public async Task FlushToDbAsync_RegistersWithMappedTotals_AndSetsInvId()
+    {
+        var (svc, inv, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var result = await svc.FlushToDbAsync(s.Token, "user1", null!);
+
+        Assert.NotNull(result);
+        Assert.Equal("INV42", result!.Id);
+        Assert.False(inv.LastChange);   // new draft (no prior InvId) → create, not update
+        Assert.Equal("INV42", svc.Get(s.Token)!.InvId);
+
+        var prms = inv.Registered!.BuildInvoiceParams(change: false, invId: "");
+        var balance = prms.First(p => p.ParameterName == "@InvoiceBalance");
+        Assert.Equal("119", System.Convert.ToString(balance.Value, System.Globalization.CultureInfo.InvariantCulture));
+        var vatRate = prms.First(p => p.ParameterName == "@InvoiceVAT_1");
+        Assert.Equal("19", vatRate.Value);
+    }
+
+    [Fact]
+    public void GetHistory_UnknownToken_IsEmpty()
+    {
+        var (svc, _, _) = NewService();
+        Assert.Empty(svc.GetHistory("ghost"));
+    }
+
+    [Theory]
+    [InlineData("address", "invoiceaddress")]
+    [InlineData("title", "invoicetitle")]
+    [InlineData("provisionperiod", "provisionperiod")]
+    public void ApplyPatch_ScalarFieldDeltas_UpdateNew(string target, string newKey)
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = target, Value = JToken.FromObject("X-VALUE") });
+
+        Assert.Equal("X-VALUE", s2!.New[newKey]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_ProvisionLocation_MirrorsLocAndProvisionlocation()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "provisionlocation", Value = JToken.FromObject("Baustelle 7") });
+
+        Assert.Equal("Baustelle 7", s2!.New["provisionlocation"]!.Value<string>());
+        Assert.Equal("Baustelle 7", s2.New["loc"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_Contact_BuildsCustomValuesJson()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta
+        {
+            Target = "contact",
+            Value = JObject.Parse(@"{'name':'Max Mustermann','email':'max@kunde.de'}")
+        });
+
+        var cv = JObject.Parse(s2!.New["CustomValues"]!.Value<string>()!);
+        Assert.Equal("Max Mustermann", cv["contactName"]!.Value<string>());
+        Assert.Equal("max@kunde.de", cv["contactEmail"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_SetmodeDelta_UpdatesAdmin()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "setmode", Value = JToken.FromObject("itemprices") });
+
+        Assert.Equal("itemprices", s2!.Admin["setmode"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_P13bExplicitFalse_TurnsOffAndRestoresVat()
+    {
+        var (svc, _, _) = NewService();
+        var payload = Payload();
+        payload["admin"]!["p13b"] = true;                    // start reverse-charge
+        var s = svc.OpenFromPayload(payload, "user1");
+        Assert.Empty(s.Sums.VatByRate);
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "p13b", Value = JToken.FromObject(false) });
+
+        Assert.Equal(119m, s2!.Sums.TotalGross);             // VAT restored
+        Assert.Equal(19m, s2.Sums.VatByRate["19"]);
+    }
+
+    [Fact]
+    public void ApplyPatch_BlockReplace_InsertsWhenBlockIsNew()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var newBlock = JObject.Parse(@"{'Id':'2','text':'Zusatz','itm':[{'id':'950','typ':'material','vt':30,'vv':5.7,'vat':'19%'}],
+                                        'items':[{'id':'950','type':'material','total_net':30,'vat':'19%'}]}");
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.replace", Ref = "2", Value = newBlock });
+
+        Assert.Equal(2, s2!.Req.Count);
+        Assert.Equal(130m, s2.Sums.TotalNet);                // 100 (block 1) + 30 (new block 2)
+        Assert.Equal(30m, s2.Sums.NetByBlock["2"]);
+    }
+
+    [Fact]
+    public void ApplyPatch_UnknownTarget_IsNoOp_NoVersionBumpNoHistory()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "nonsense", Value = JToken.FromObject("x") });
+
+        Assert.NotNull(s2);
+        Assert.Equal(0, s2!.Version);
+        Assert.Empty(s2.History);
+    }
+
+    [Fact]
+    public void ApplyPatch_MultipleEdits_AccumulateHistoryInOrder()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "email", Value = JToken.FromObject("a1@x.de") });
+        svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "title", Value = JToken.FromObject("Titel 2") });
+        var s3 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "address", Value = JToken.FromObject("Adr 3") });
+
+        Assert.Equal(3, s3!.Version);
+        Assert.Equal(3, s3.History.Count);
+        Assert.Equal(new[] { "email", "title", "address" }, s3.History.Select(h => h.Target).ToArray());
+        Assert.Equal(new[] { 1, 2, 3 }, s3.History.Select(h => h.Version).ToArray());
+    }
+
+    [Fact]
+    public void BuildState_ExposesPayloadSumsValidationAndVersion()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+        svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "email", Value = JToken.FromObject("x@y.de") });
+
+        var state = JObject.FromObject(svc.BuildState(svc.Get(s.Token)!));
+
+        Assert.Equal(1, state["version"]!.Value<int>());
+        Assert.Equal(100m, state["sums"]!["total_net"]!.Value<decimal>());
+        Assert.Equal(119m, state["sums"]!["total_gross"]!.Value<decimal>());
+        Assert.Equal(19m, state["sums"]!["vat"]!["19"]!.Value<decimal>());
+        Assert.Single((JArray)state["req"]!);
+        Assert.Equal(1, state["historyCount"]!.Value<int>());
+        Assert.NotNull(state["validation"]);
+    }
+
+    [Fact]
+    public async Task FlushToDbAsync_ExistingInvId_UpdatesInsteadOfCreates()
+    {
+        var (svc, inv, _) = NewService();
+        var payload = Payload();
+        payload["invid"] = "INV7";
+        var s = svc.OpenFromPayload(payload, "user1");
+
+        await svc.FlushToDbAsync(s.Token, "user1", null!);
+
+        Assert.True(inv.LastChange);   // prior InvId → update path
+    }
+
+    [Fact]
+    public async Task FlushToDbAsync_MapsInvoiceOptionsFrom13bAndSetmode()
+    {
+        var (svc, inv, _) = NewService();
+        var payload = Payload();
+        payload["admin"]!["p13b"] = true;
+        payload["admin"]!["setmode"] = "itemprices";
+        var s = svc.OpenFromPayload(payload, "user1");
+
+        await svc.FlushToDbAsync(s.Token, "user1", null!);
+
+        var options = inv.Registered!.BuildInvoiceParams(change: false, invId: "")
+            .First(p => p.ParameterName == "@InvoiceOptions").Value?.ToString() ?? "";
+        Assert.Contains("§13b", options);
+        Assert.Contains("setmode:itemprices", options);
+    }
+
+    [Fact]
+    public void RenderPreview_SynthesizesDraftRegistrationFromSession()
+    {
+        var (svc, inv, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var doc = svc.RenderPreview(s.Token);
+
+        Assert.NotNull(doc);
+        Assert.True(inv.PreviewDraft);                          // always rendered as a draft
+        var reg = inv.PreviewInvoice!.InvoiceRegistration!;
+        Assert.Equal("Rechnung", reg.getString("InvoiceTitle"));
+        Assert.Equal("Weg 1", reg.getString("SendToAddress"));
+        Assert.Equal("a@b.de", reg.getString("SendToEmail"));
+        Assert.Equal("19", reg.getString("InvoiceVAT_1"));     // rate synthesised from server sums
+        Assert.True(inv.PreviewInvoice.IsDraft);
+    }
+
+    [Fact]
+    public void RenderPreview_UnknownToken_ReturnsNull()
+    {
+        var (svc, _, _) = NewService();
+        Assert.Null(svc.RenderPreview("ghost"));
+    }
+
+    [Fact]
+    public void Close_RemovesSession_ThenReportsFalse()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        Assert.True(svc.Close(s.Token));
+        Assert.Null(svc.Get(s.Token));
+        Assert.False(svc.Close(s.Token));
+    }
+
+    // ── HTML sanitisation (values must never reach the DB/PDF wrapped in tags) ─
+    [Theory]
+    [InlineData("provisionperiod", "provisionperiod")]
+    [InlineData("title", "invoicetitle")]
+    [InlineData("email", "invoiceemail")]
+    public void ApplyPatch_ScalarField_StripsHtmlWrapper(string target, string newKey)
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = target, Value = JToken.FromObject("<p>18.06.2026</p>") });
+
+        Assert.Equal("18.06.2026", s2!.New[newKey]!.Value<string>());   // no <p> tags stored
+        Assert.Equal("18.06.2026", Assert.Single(s2.History).NewValue);
+    }
+
+    [Fact]
+    public void ApplyPatch_Address_MultilineHtml_KeepsLineBreaks()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta
+        {
+            Target = "address",
+            Value = JToken.FromObject("<p>Firma AG</p><p>Weg 1<br>5080 Laufenburg</p>")
+        });
+
+        Assert.Equal("Firma AG\nWeg 1\n5080 Laufenburg", s2!.New["invoiceaddress"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_ScalarField_DecodesEntities()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "title", Value = JToken.FromObject("Tom &amp; Jerry") });
+
+        Assert.Equal("Tom & Jerry", s2!.New["invoicetitle"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_ProvisionLocation_SanitisesAndMirrorsLoc()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "provisionlocation", Value = JToken.FromObject("<p>Baustelle 7</p>") });
+
+        Assert.Equal("Baustelle 7", s2!.New["provisionlocation"]!.Value<string>());
+        Assert.Equal("Baustelle 7", s2.New["loc"]!.Value<string>());
+    }
+
+    // ── Change history records the changed field, not the whole block JSON ─────
+    [Fact]
+    public void ApplyPatch_BlockReplace_HistoryNewValueIsSectionText_NotJson()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var newBlock = JObject.Parse(@"{'Id':'1','text':'<p>Neue Überschrift</p>',
+            'itm':[{'id':'900','typ':'material','vt':100,'vv':19,'vat':'19%'}],
+            'items':[{'id':'900','type':'material','total_net':100,'vat':'19%'}]}");
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.replace", Ref = "1", Value = newBlock });
+
+        var h = Assert.Single(s2!.History);
+        Assert.Equal("Neue Überschrift", h.NewValue);      // the heading, sanitised — never the block JSON
+        Assert.DoesNotContain("{", h.NewValue);
+        Assert.Equal("Auftrag", h.OldValue);
+        // and the cached block text is stored clean too
+        Assert.Equal("Neue Überschrift", ((JObject)s2.Req[0])["text"]!.Value<string>());
+    }
+
+    // ── Section reorder ───────────────────────────────────────────────────────
+    private static JObject TwoBlockPayload() => JObject.Parse(@"{
+        'admin':{'p13b':false,'type':'r'},
+        'new':{'invoiceemail':'a@b.de','invoiceaddress':'Weg 1'},
+        'req':[
+          {'Id':'1','text':'A','itm':[{'id':'900','typ':'material','vt':100,'vv':19,'vat':'19%'}],'items':[{'id':'900','type':'material','total_net':100,'vat':'19%'}]},
+          {'Id':'2','text':'B','itm':[{'id':'950','typ':'material','vt':30,'vv':5.7,'vat':'19%'}],'items':[{'id':'950','type':'material','total_net':30,'vat':'19%'}]}
+        ]}");
+
+    [Fact]
+    public void ApplyPatch_BlockOrder_ReordersReqAndRenumbersPositions()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(TwoBlockPayload(), "user1");
+        Assert.Equal(new[] { "1", "2" }, s.Req.Select(b => b["Id"]!.Value<string>()).ToArray());
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.order", Value = JArray.Parse("['2','1']") });
+
+        Assert.Equal(new[] { "2", "1" }, s2!.Req.Select(b => b["Id"]!.Value<string>()).ToArray());
+        Assert.Equal("1", ((JObject)((JArray)((JObject)s2.Req[0])["itm"]!)[0])["p"]!.ToString());   // block 2's item now position 1
+        Assert.Equal(130m, s2.Sums.TotalNet);                                                        // totals unaffected by reorder
+        var h = Assert.Single(s2.History);
+        Assert.Equal("1,2", h.OldValue);
+        Assert.Equal("2,1", h.NewValue);
+    }
+
+    [Fact]
+    public void ApplyPatch_BlockOrder_UnchangedSequence_IsNoOp()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(TwoBlockPayload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.order", Value = JArray.Parse("['1','2']") });
+
+        Assert.Equal(0, s2!.Version);      // no-op: no version bump, no history
+        Assert.Empty(s2.History);
+    }
+
+    [Fact]
+    public void ApplyPatch_BlockOrder_UnknownIds_KeepMentionedFirstThenRest()
+    {
+        var (svc, _, _) = NewService();
+        var s = svc.OpenFromPayload(TwoBlockPayload(), "user1");
+
+        // Only name block 2; block 1 is unmentioned and must be kept (appended after).
+        var s2 = svc.ApplyPatch(s.Token, new InvoiceDraftDelta { Target = "block.order", Value = JArray.Parse("['2','ghost']") });
+
+        Assert.Equal(new[] { "2", "1" }, s2!.Req.Select(b => b["Id"]!.Value<string>()).ToArray());
+    }
+}

Fuchs.Tests/ReminderDraftCalculatorTests.cs

@@ -0,0 +1,92 @@
+using Fuchs.intranet;
+using Newtonsoft.Json.Linq;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Exhaustively exercises the pure reminder-draft aggregation/validation (ADR 0006,
+/// the reminder mirror of <see cref="InvoiceDraftCalculatorTests"/>). Being static/pure,
+/// the open-amount math and the plausibility checks are unit-testable without a DB.
+/// </summary>
+public class ReminderDraftCalculatorTests
+{
+    private static ReminderDraftSession Session(string newJson) =>
+        new() { New = JObject.Parse(newJson) };
+
+    [Theory]
+    [InlineData("{'amount':119,'amount_payed':0}", 119, 0, 119)]
+    [InlineData("{'amount':119,'amount_payed':20}", 119, 20, 99)]
+    [InlineData("{'amount':'119,50','amount_payed':'19,50'}", 119.50, 19.50, 100)]   // German decimals
+    [InlineData("{'amount':'100.00','amount_payed':'40.00'}", 100, 40, 60)]          // invariant decimals
+    [InlineData("{}", 0, 0, 0)]                                                       // missing → 0
+    [InlineData("{'amount':50,'amount_payed':80}", 50, 80, -30)]                      // overpaid → negative
+    public void RecomputeTotals_ComputesOpenAmount(string newJson, double total, double payed, double open)
+    {
+        var s = Session(newJson);
+        ReminderDraftCalculator.RecomputeTotals(s);
+        Assert.Equal((decimal)total, s.Sums.AmountTotal);
+        Assert.Equal((decimal)payed, s.Sums.AmountPayed);
+        Assert.Equal((decimal)open,  s.Sums.AmountOpen);
+    }
+
+    [Fact]
+    public void Validate_EmptyEmail_Warns()
+    {
+        var s = Session("{'amount':119,'invoiceaddress':'Weg 1','subject':'X'}");
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "email" && m.Severity == "warning");
+    }
+
+    [Theory]
+    [InlineData("bad")]
+    [InlineData("no-at-sign.de")]
+    [InlineData("trailing@dot.")]
+    public void Validate_InvalidEmail_Errors(string email)
+    {
+        var s = Session($"{{'amount':119,'invoiceemail':'{email}','invoiceaddress':'Weg 1','subject':'X'}}");
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "email" && m.Severity == "error");
+    }
+
+    [Fact]
+    public void Validate_ValidEmail_NoEmailMessage()
+    {
+        var s = Session("{'amount':119,'invoiceemail':'a@b.de','invoiceaddress':'Weg 1','subject':'X'}");
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.DoesNotContain(s.ValidationMessages, m => m.Field == "email");
+    }
+
+    [Fact]
+    public void Validate_EmptyAddressAndSubject_Warn()
+    {
+        var s = Session("{'amount':119,'invoiceemail':'a@b.de'}");
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "address" && m.Severity == "warning");
+        Assert.Contains(s.ValidationMessages, m => m.Field == "subject" && m.Severity == "warning");
+    }
+
+    [Theory]
+    [InlineData("{'amount':0,'amount_payed':0,'invoiceemail':'a@b.de','invoiceaddress':'W','subject':'X'}")]
+    [InlineData("{'amount':50,'amount_payed':80,'invoiceemail':'a@b.de','invoiceaddress':'W','subject':'X'}")]
+    public void Validate_NonPositiveOpenAmount_Warns(string newJson)
+    {
+        var s = Session(newJson);
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.Contains(s.ValidationMessages, m => m.Field == "amount" && m.Severity == "warning");
+    }
+
+    [Fact]
+    public void Validate_HealthyDraft_HasNoMessages()
+    {
+        var s = Session("{'amount':119,'amount_payed':0,'invoiceemail':'a@b.de','invoiceaddress':'Weg 1','subject':'Zahlungserinnerung'}");
+        ReminderDraftCalculator.RecomputeTotals(s);
+        ReminderDraftCalculator.Validate(s);
+        Assert.Empty(s.ValidationMessages);
+    }
+}

Fuchs.Tests/ReminderDraftServiceTests.cs

@@ -0,0 +1,307 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Fuchs.intranet;
+using Fuchs.Services;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+using Xunit;
+using static OCORE.OCORE_dictionaries;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Exercises the reminder draft edit orchestrator's pure paths (open/patch/history/flush)
+/// without a database — the reminder mirror of <see cref="InvoiceDraftServiceTests"/>,
+/// proving the backend-authoritative model behaves correctly at the service seam (ADR 0006).
+/// </summary>
+public class ReminderDraftServiceTests
+{
+    /// <summary>Captures the reminder handed to registration and returns it with a fake DB id — no SQL.</summary>
+    private sealed class FakeReminderService : IReminderService
+    {
+        public FdsReminderData? Registered;
+        public bool? LastChange;
+        public FdsReminderData? PreviewReminder;
+        public bool? PreviewDraft;
+
+        public Task<FdsReminderData> RegisterReminderAsync(FdsReminderData reminder, bool change, string remId, string userAccountId, DatabaseSecurity dbSec)
+        {
+            Registered = reminder;
+            LastChange = change;
+            reminder.ReminderRegistration = new GenericObjectDictionary(new System.Collections.Generic.Dictionary<string, object> { ["Id"] = "REM42" });
+            return Task.FromResult(reminder);
+        }
+        public Document GenerateReminderPdf(FdsReminderData reminder, bool draft) { PreviewReminder = reminder; PreviewDraft = draft; return new Document(); }
+        public Task<FdsReminderData> LoadReminderAsync(string id, string u, DatabaseSecurity s) => throw new NotSupportedException();
+        public Task<byte[]> RenderReminderPdfBytesAsync(FdsReminderData r, bool d) => throw new NotSupportedException();
+        public Task<byte[]> StoreReminderDocumentFileAsync(FdsReminderData r, bool d, string u, DatabaseSecurity s) => throw new NotSupportedException();
+        public Task<byte[]> GetReminderFileAsync(FdsReminderData r, bool d, fds.IFdsMfr m, string u, DatabaseSecurity s) => throw new NotSupportedException();
+        public Task<(System.IO.FileInfo? file, byte[]? content)> GetStoredFileAsync(string id, string u, DatabaseSecurity s) => throw new NotSupportedException();
+    }
+
+    private static (ReminderDraftEditService svc, FakeReminderService rem) NewService()
+    {
+        var cache = new ReminderDraftCache(new ConfigurationBuilder().Build());
+        var rem = new FakeReminderService();
+        var svc = new ReminderDraftEditService(cache, rem, NullLogger<ReminderDraftEditService>.Instance);
+        return (svc, rem);
+    }
+
+    private static JObject Payload() => JObject.Parse(@"{
+        'rem':{'invid':'INV5','type':'R','invoiceid':'R2026-1','invoicedate':'2026-06-01'},
+        'new':{'invoiceemail':'a@b.de','invoiceaddress':'Weg 1','subject':'Zahlungserinnerung','amount':119,'amount_payed':0}
+    }");
+
+    [Fact]
+    public void OpenFromPayload_SeedsSessionAndComputesOpenAmount()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+        Assert.False(string.IsNullOrEmpty(s.Token));
+        Assert.Equal(0, s.Version);
+        Assert.Equal(119m, s.Sums.AmountTotal);
+        Assert.Equal(119m, s.Sums.AmountOpen);
+    }
+
+    [Fact]
+    public void ApplyPatch_Email_MutatesBumpsVersionAndRecordsHistory()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "email", Value = JToken.FromObject("neu@x.de") });
+
+        Assert.NotNull(s2);
+        Assert.Equal(1, s2!.Version);
+        Assert.Equal("neu@x.de", s2.New["invoiceemail"]!.Value<string>());
+        var h = Assert.Single(s2.History);
+        Assert.Equal("email", h.Target);
+        Assert.Equal("a@b.de", h.OldValue);
+        Assert.Equal("neu@x.de", h.NewValue);
+    }
+
+    [Fact]
+    public void ApplyPatch_Amount_RecomputesOpenAmount()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "amount", Value = JToken.FromObject(200) });
+
+        Assert.Equal(200m, s2!.Sums.AmountTotal);
+        Assert.Equal(200m, s2.Sums.AmountOpen);
+    }
+
+    [Fact]
+    public void ApplyPatch_AmountPayed_RecomputesOpenAmount()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "amount_payed", Value = JToken.FromObject(19) });
+
+        Assert.Equal(100m, s2!.Sums.AmountOpen);   // 119 - 19
+    }
+
+    [Fact]
+    public void ApplyPatch_AmountFromGermanString_NormalisesToInvariant()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "amount", Value = JToken.FromObject("249,90") });
+
+        Assert.Equal("249.90", s2!.New["amount"]!.Value<string>());   // stored invariant
+        Assert.Equal(249.90m, s2.Sums.AmountTotal);
+    }
+
+    [Fact]
+    public void ApplyPatch_UnknownToken_ReturnsNull()
+    {
+        var (svc, _) = NewService();
+        Assert.Null(svc.ApplyPatch("ghost", new ReminderDraftDelta { Target = "email", Value = JToken.FromObject("x@y.de") }));
+    }
+
+    [Fact]
+    public void ApplyPatch_UnknownTarget_IsNoOp()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "nonsense", Value = JToken.FromObject("x") });
+
+        Assert.Equal(0, s2!.Version);
+        Assert.Empty(s2.History);
+    }
+
+    [Theory]
+    [InlineData("subject", "subject")]
+    [InlineData("address", "invoiceaddress")]
+    [InlineData("text", "text")]
+    public void ApplyPatch_ScalarFieldDeltas_UpdateNew(string target, string newKey)
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = target, Value = JToken.FromObject("X-VALUE") });
+
+        Assert.Equal("X-VALUE", s2!.New[newKey]!.Value<string>());
+    }
+
+    [Theory]
+    [InlineData("subject", "subject")]
+    [InlineData("email", "invoiceemail")]
+    public void ApplyPatch_ScalarField_StripsHtmlWrapper(string target, string newKey)
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = target, Value = JToken.FromObject("<p>clean me</p>") });
+
+        Assert.Equal("clean me", s2!.New[newKey]!.Value<string>());
+        Assert.DoesNotContain("<", s2.New[newKey]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_Address_MultilineHtml_KeepsLineBreaks()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta
+        {
+            Target = "address",
+            Value = JToken.FromObject("<p>Firma AG</p><p>Weg 1<br>40000 Düsseldorf</p>")
+        });
+
+        Assert.Equal("Firma AG\nWeg 1\n40000 Düsseldorf", s2!.New["invoiceaddress"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_Contact_BuildsCustomValuesJson()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var s2 = svc.ApplyPatch(s.Token, new ReminderDraftDelta
+        {
+            Target = "contact",
+            Value = JObject.Parse(@"{'name':'Max Mustermann','email':'max@kunde.de'}")
+        });
+
+        var cv = JObject.Parse(s2!.New["CustomValues"]!.Value<string>()!);
+        Assert.Equal("Max Mustermann", cv["contactName"]!.Value<string>());
+        Assert.Equal("max@kunde.de", cv["contactEmail"]!.Value<string>());
+    }
+
+    [Fact]
+    public void ApplyPatch_MultipleEdits_AccumulateHistoryInOrder()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "email", Value = JToken.FromObject("a1@x.de") });
+        svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "subject", Value = JToken.FromObject("Mahnung 2") });
+        var s3 = svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "amount", Value = JToken.FromObject(200) });
+
+        Assert.Equal(3, s3!.Version);
+        Assert.Equal(new[] { "email", "subject", "amount" }, s3.History.Select(h => h.Target).ToArray());
+        Assert.Equal(new[] { 1, 2, 3 }, s3.History.Select(h => h.Version).ToArray());
+    }
+
+    [Fact]
+    public void BuildState_ExposesPayloadSumsValidationAndVersion()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+        svc.ApplyPatch(s.Token, new ReminderDraftDelta { Target = "amount_payed", Value = JToken.FromObject(19) });
+
+        var state = JObject.FromObject(svc.BuildState(svc.Get(s.Token)!));
+
+        Assert.Equal(1, state["version"]!.Value<int>());
+        Assert.Equal(119m, state["sums"]!["amount_total"]!.Value<decimal>());
+        Assert.Equal(100m, state["sums"]!["amount_open"]!.Value<decimal>());
+        Assert.Equal(1, state["historyCount"]!.Value<int>());
+        Assert.NotNull(state["validation"]);
+    }
+
+    [Fact]
+    public async Task FlushToDbAsync_RegistersAndSetsRemId_CreatePath()
+    {
+        var (svc, rem) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var result = await svc.FlushToDbAsync(s.Token, "user1", null!);
+
+        Assert.NotNull(result);
+        Assert.Equal("REM42", result!.Id);
+        Assert.False(rem.LastChange);   // new draft (no prior RemId) → create
+        Assert.Equal("REM42", svc.Get(s.Token)!.RemId);
+        // the email/subject the editor set must reach registration
+        Assert.Equal("a@b.de", rem.Registered!.RawInvoiceEmail);
+        Assert.Equal("Zahlungserinnerung", rem.Registered!.NewValues!.getString("subject"));
+        Assert.Equal("INV5", rem.Registered!.RawInvId);
+    }
+
+    [Fact]
+    public async Task FlushToDbAsync_ExistingRemId_UpdatePath()
+    {
+        var (svc, rem) = NewService();
+        var payload = Payload();
+        payload["remid"] = "REM7";
+        var s = svc.OpenFromPayload(payload, "user1");
+
+        await svc.FlushToDbAsync(s.Token, "user1", null!);
+
+        Assert.True(rem.LastChange);   // prior RemId → update path
+    }
+
+    [Fact]
+    public void RenderPreview_SynthesizesDraftRegistrationFromSession()
+    {
+        var (svc, rem) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        var doc = svc.RenderPreview(s.Token);
+
+        Assert.NotNull(doc);
+        Assert.True(rem.PreviewDraft);
+        Assert.True(rem.PreviewReminder!.IsDraft);
+        var reg = rem.PreviewReminder!.ReminderRegistration!;
+        Assert.Equal("Zahlungserinnerung", reg.getString("subject"));
+        Assert.Equal("Weg 1", reg.getString("SendToAddress"));
+        Assert.Equal("a@b.de", reg.getString("SendToEmail"));
+        Assert.Equal("R2026-1", reg.getString("InvoiceId"));
+        // the synthesised single-invoice row the reminder table renders
+        Assert.Single(rem.PreviewReminder!.ReminderItems);
+    }
+
+    [Fact]
+    public void RenderPreview_UnknownToken_ReturnsNull()
+    {
+        var (svc, _) = NewService();
+        Assert.Null(svc.RenderPreview("ghost"));
+    }
+
+    [Fact]
+    public void GetHistory_UnknownToken_IsEmpty()
+    {
+        var (svc, _) = NewService();
+        Assert.Empty(svc.GetHistory("ghost"));
+    }
+
+    [Fact]
+    public void Close_RemovesSession_ThenReportsFalse()
+    {
+        var (svc, _) = NewService();
+        var s = svc.OpenFromPayload(Payload(), "user1");
+
+        Assert.True(svc.Close(s.Token));
+        Assert.Null(svc.Get(s.Token));
+        Assert.False(svc.Close(s.Token));
+    }
+}

Fuchs/Controllers/IntranetController.InvoiceDraft.cs

@@ -0,0 +1,130 @@
+using Fuchs.intranet;
+using Fuchs.Services;
+using Microsoft.AspNetCore.Mvc;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using static OCORE.web.mvc_helper_async;
+
+namespace Fuchs.Controllers;
+
+// Partial class: live, backend-authoritative invoice draft editing (ADR 0006).
+// The browser posts single edits here; the server mutates the in-memory session
+// (the source of truth), recomputes/validates, and pings the editing browser over
+// SignalR (draftReady) to re-fetch. Commands are ordinary POSTs — the hub carries
+// only signals (ADR 0007).
+public partial class IntranetController
+{
+    /// <summary>Standard 410 when a session token is unknown/expired — the client re-opens the draft.</summary>
+    private IActionResult DraftGone() => StatusCode(410, new { error = "expired" });
+
+    // POST inv/dopen — { payload } → { token, version }
+    // The editor assembles the initial draft (from a service request or a reloaded DB draft
+    // via the existing render paths) and seeds the authoritative session here. Reload/discard
+    // is the client re-fetching + re-seeding, so there is no server-side DB reshaping.
+    private async Task<IActionResult> HandleDraftOpen(string fn, string id, string code)
+    {
+        if (!HasForm("payload"))
+        {
+            _logger.LogWarning("Draft dopen: 'payload' missing user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        JObject payload;
+        try { payload = JObject.Parse(Form("payload")); }
+        catch (JsonException ex)
+        {
+            _logger.LogWarning(ex, "Draft dopen: invalid payload JSON user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        var session = _invoiceDrafts.OpenFromPayload(payload, UserAccountID);
+        _logger.LogInformation("Draft dopen: session {Token} (invId={InvId}) user={User}", session.Token, session.InvId, UserAccountID);
+        // The browser holds the token from this response and fetches dstate directly; there is
+        // no server 'draftReady' on open (it would race the client's group-join). Signals drive
+        // only subsequent server-side changes.
+        return await JSONAsync(new { token = session.Token, version = session.Version });
+    }
+
+    // POST inv/dstate — { token } → full view state
+    private async Task<IActionResult> HandleDraftState(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        var session = _invoiceDrafts.Get(Form("token"));
+        if (session == null) return DraftGone();
+        return await JSONAsync(_invoiceDrafts.BuildState(session));
+    }
+
+    // POST inv/dpatch — { token, delta } → { ok, version }; signals draftReady
+    private async Task<IActionResult> HandleDraftPatch(string fn, string id, string code)
+    {
+        if (!HasForm("token", "delta")) return BadRequest400();
+        InvoiceDraftDelta? delta;
+        try { delta = JsonConvert.DeserializeObject<InvoiceDraftDelta>(Form("delta")); }
+        catch (JsonException ex)
+        {
+            _logger.LogWarning(ex, "Draft dpatch: invalid delta JSON user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        if (delta == null || string.IsNullOrEmpty(delta.Target)) return BadRequest400();
+
+        var session = _invoiceDrafts.ApplyPatch(Form("token"), delta);
+        if (session == null) return DraftGone();
+        await _draftNotifier.SignalDraftReadyAsync(session.Token, session.Version);
+        return await JSONAsync(new { ok = true, version = session.Version });
+    }
+
+    // POST inv/dpreview — { token } → { img[], total } (rendered straight from the cache)
+    private async Task<IActionResult> HandleDraftPreview(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        var doc = _invoiceDrafts.RenderPreview(Form("token"));
+        if (doc == null) return DraftGone();
+        var imgcol = await _pdf.DocToImageCollectionAsync(doc);
+        return await JSONAsync(new { img = imgcol.ImgB64Array, total = imgcol.TotalPages });
+    }
+
+    // POST inv/dsave — { token } → { ok, invid }; flush cache→DB + business event + draftReady
+    private async Task<IActionResult> HandleDraftSave(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        string token = Form("token");
+        var before = _invoiceDrafts.Get(token);
+        if (before == null) return DraftGone();
+        bool existed = !string.IsNullOrEmpty(before.InvId);
+
+        var fdInv = await _invoiceDrafts.FlushToDbAsync(token, UserAccountID, DbSec);
+        if (fdInv == null) return DraftGone();
+        if (string.IsNullOrEmpty(fdInv.Id))
+            return await InvoiceIssueResult("Der Zwischenstand konnte aufgrund eines Fehlers nicht gespeichert werden.");
+
+        await _events.InvoiceDraftRegisteredAsync(fdInv, existed, UserAccountID);
+        var after = _invoiceDrafts.Get(token);
+        if (after != null) await _draftNotifier.SignalDraftReadyAsync(after.Token, after.Version);
+        return await JSONAsync(new { ok = true, invid = fdInv.Id });
+    }
+
+    // POST inv/dhistory — { token } → { history[] }
+    private async Task<IActionResult> HandleDraftHistory(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        if (_invoiceDrafts.Get(Form("token")) == null) return DraftGone();
+        var history = _invoiceDrafts.GetHistory(Form("token"))
+            .Select(h => new
+            {
+                timestamp = h.TimestampUtc,
+                target    = h.Target,
+                @ref      = h.Ref,
+                oldValue  = h.OldValue,
+                newValue  = h.NewValue,
+                version   = h.Version
+            });
+        return await JSONAsync(new { history });
+    }
+
+    // POST inv/dclose — { token } → { ok }
+    private async Task<IActionResult> HandleDraftClose(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        bool ok = _invoiceDrafts.Close(Form("token"));
+        _logger.LogDebug("Draft dclose token={Token} removed={Removed} user={User}", Form("token"), ok, UserAccountID);
+        return await JSONAsync(new { ok });
+    }
+}

Fuchs/Controllers/IntranetController.Invoices.cs

@@ -158,6 +158,15 @@ public partial class IntranetController
                         fds.FdsMfr.UpdateNeed.Reset, new[] { relId });
                 return await JSONAsync(new { ok = true });
 
+            // ── Live backend-authoritative draft editing (ADR 0006) ───────────
+            case "dopen":    return await HandleDraftOpen(fn, id, code);
+            case "dstate":   return await HandleDraftState(fn, id, code);
+            case "dpatch":   return await HandleDraftPatch(fn, id, code);
+            case "dpreview": return await HandleDraftPreview(fn, id, code);
+            case "dsave":    return await HandleDraftSave(fn, id, code);
+            case "dhistory": return await HandleDraftHistory(fn, id, code);
+            case "dclose":   return await HandleDraftClose(fn, id, code);
+
             default:
                 _logger.LogWarning("Do_Process_Invoices: unhandled action id={Id}, user={User}", id, UserAccountID);
                 return await JSONAsync(new { ok = true });

Fuchs/Controllers/IntranetController.Reminder.cs

@@ -97,6 +97,15 @@ public partial class IntranetController
             case "idoc":   return await HandleReminderIdoc(fn, id, code);
             case "resend": return await HandleReminderResend(fn, id, code);
 
+            // ── Live backend-authoritative draft editing (ADR 0006) ───────────
+            case "dopen":    return await HandleReminderDraftOpen(fn, id, code);
+            case "dstate":   return await HandleReminderDraftState(fn, id, code);
+            case "dpatch":   return await HandleReminderDraftPatch(fn, id, code);
+            case "dpreview": return await HandleReminderDraftPreview(fn, id, code);
+            case "dsave":    return await HandleReminderDraftSave(fn, id, code);
+            case "dhistory": return await HandleReminderDraftHistory(fn, id, code);
+            case "dclose":   return await HandleReminderDraftClose(fn, id, code);
+
             case "lrem":
             {
                 if (!HasForm("id")) { _logger.LogWarning("Reminder lrem: missing form field 'id', user={User}", UserAccountID); return BadRequest400(); }

Fuchs/Controllers/IntranetController.ReminderDraft.cs

@@ -0,0 +1,122 @@
+using Fuchs.Services;
+using Microsoft.AspNetCore.Mvc;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using static OCORE.web.mvc_helper_async;
+
+namespace Fuchs.Controllers;
+
+// Partial class: live, backend-authoritative reminder draft editing (ADR 0006) — the
+// reminder mirror of IntranetController.InvoiceDraft.cs. The browser posts single edits
+// here; the server mutates the in-memory session (the source of truth), recomputes the
+// open amount / validates, and pings the editing browser over the shared DraftPreviewHub
+// (draftReady) to re-fetch. Commands are ordinary POSTs — the hub carries only signals.
+public partial class IntranetController
+{
+    // POST rem/dopen — { payload } → { token, version }
+    private async Task<IActionResult> HandleReminderDraftOpen(string fn, string id, string code)
+    {
+        if (!HasForm("payload"))
+        {
+            _logger.LogWarning("Reminder draft dopen: 'payload' missing user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        JObject payload;
+        try { payload = JObject.Parse(Form("payload")); }
+        catch (JsonException ex)
+        {
+            _logger.LogWarning(ex, "Reminder draft dopen: invalid payload JSON user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        var session = _reminderDrafts.OpenFromPayload(payload, UserAccountID);
+        _logger.LogInformation("Reminder draft dopen: session {Token} (remId={RemId}) user={User}", session.Token, session.RemId, UserAccountID);
+        // The browser holds the token from this response and fetches dstate directly; there is
+        // no server 'draftReady' on open (it would race the client's group-join).
+        return await JSONAsync(new { token = session.Token, version = session.Version });
+    }
+
+    // POST rem/dstate — { token } → full view state
+    private async Task<IActionResult> HandleReminderDraftState(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        var session = _reminderDrafts.Get(Form("token"));
+        if (session == null) return DraftGone();
+        return await JSONAsync(_reminderDrafts.BuildState(session));
+    }
+
+    // POST rem/dpatch — { token, delta } → { ok, version }; signals draftReady
+    private async Task<IActionResult> HandleReminderDraftPatch(string fn, string id, string code)
+    {
+        if (!HasForm("token", "delta")) return BadRequest400();
+        ReminderDraftDelta? delta;
+        try { delta = JsonConvert.DeserializeObject<ReminderDraftDelta>(Form("delta")); }
+        catch (JsonException ex)
+        {
+            _logger.LogWarning(ex, "Reminder draft dpatch: invalid delta JSON user={User}", UserAccountID);
+            return BadRequest400();
+        }
+        if (delta == null || string.IsNullOrEmpty(delta.Target)) return BadRequest400();
+
+        var session = _reminderDrafts.ApplyPatch(Form("token"), delta);
+        if (session == null) return DraftGone();
+        await _draftNotifier.SignalDraftReadyAsync(session.Token, session.Version);
+        return await JSONAsync(new { ok = true, version = session.Version });
+    }
+
+    // POST rem/dpreview — { token } → { img[], total } (rendered straight from the cache)
+    private async Task<IActionResult> HandleReminderDraftPreview(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        var doc = _reminderDrafts.RenderPreview(Form("token"));
+        if (doc == null) return DraftGone();
+        var imgcol = await _pdf.DocToImageCollectionAsync(doc);
+        return await JSONAsync(new { img = imgcol.ImgB64Array, total = imgcol.TotalPages });
+    }
+
+    // POST rem/dsave — { token } → { ok, remid }; flush cache→DB + business event + draftReady
+    private async Task<IActionResult> HandleReminderDraftSave(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        string token = Form("token");
+        var before = _reminderDrafts.Get(token);
+        if (before == null) return DraftGone();
+        bool existed = !string.IsNullOrEmpty(before.RemId);
+
+        var fdRem = await _reminderDrafts.FlushToDbAsync(token, UserAccountID, DbSec);
+        if (fdRem == null) return DraftGone();
+        if (string.IsNullOrEmpty(fdRem.Id))
+            return await ReminderIssueResult("Der Zwischenstand konnte aufgrund eines Fehlers nicht gespeichert werden.");
+
+        await _events.ReminderDraftRegisteredAsync(fdRem, existed, UserAccountID);
+        var after = _reminderDrafts.Get(token);
+        if (after != null) await _draftNotifier.SignalDraftReadyAsync(after.Token, after.Version);
+        return await JSONAsync(new { ok = true, remid = fdRem.Id });
+    }
+
+    // POST rem/dhistory — { token } → { history[] }
+    private async Task<IActionResult> HandleReminderDraftHistory(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        if (_reminderDrafts.Get(Form("token")) == null) return DraftGone();
+        var history = _reminderDrafts.GetHistory(Form("token"))
+            .Select(h => new
+            {
+                timestamp = h.TimestampUtc,
+                target    = h.Target,
+                @ref      = h.Ref,
+                oldValue  = h.OldValue,
+                newValue  = h.NewValue,
+                version   = h.Version
+            });
+        return await JSONAsync(new { history });
+    }
+
+    // POST rem/dclose — { token } → { ok }
+    private async Task<IActionResult> HandleReminderDraftClose(string fn, string id, string code)
+    {
+        if (!HasForm("token")) return BadRequest400();
+        bool ok = _reminderDrafts.Close(Form("token"));
+        _logger.LogDebug("Reminder draft dclose token={Token} removed={Removed} user={User}", Form("token"), ok, UserAccountID);
+        return await JSONAsync(new { ok });
+    }
+}

Fuchs/Controllers/IntranetController.Requests.cs

@@ -369,6 +369,21 @@ public partial class IntranetController
         return await InvoiceIssueResult("Die Rechnung konnte aufgrund eines Fehlers nicht erstellt werden.");
     }
 
+    /// <summary>
+    /// Serves the PDF inline (browser shows it) while advertising the real download filename —
+    /// both a quoted ASCII form and RFC 5987 <c>filename*</c> for spaces/non-ASCII. Works around
+    /// the OCORE FileContentResult helper, whose classic-MVC <c>ExecuteResult(ControllerContext)</c>
+    /// never runs under ASP.NET Core, so the filename was dropped and downloads used the "idoc"
+    /// endpoint segment.
+    /// </summary>
+    private void SetInlinePdfFilename(string filename)
+    {
+        string safe = (filename ?? "").Replace("\"", "").Replace("\r", " ").Replace("\n", " ").Trim();
+        if (safe.Length == 0) return;
+        Response.Headers["Content-Disposition"] =
+            $"inline; filename=\"{safe}\"; filename*=UTF-8''{Uri.EscapeDataString(safe)}";
+    }
+
     private async Task<IActionResult> HandleRequestIdoc(string fn, string id, string code)
     {
         if (!HasForm("id") || string.IsNullOrEmpty(Form("id"))) { _logger.LogWarning("HandleRequestIdoc: missing/empty form field 'id', user={User}", UserAccountID); return StatusCode(404); }
@@ -381,9 +396,13 @@ public partial class IntranetController
             byte[]? ct = Form("create", "0") != "1"
                 ? await _invoices.GetInvoiceFileAsync(fdInv, fdInv.IsDraft, _mfr) is { Length: > 0 } f1 ? f1 : await _invoices.StoreInvoiceDocumentFileAsync(fdInv, fdInv.IsDraft, UserAccountID, DbSec)
                 : _pdf.DocToPdfBytes(_invoices.GenerateInvoicePdf(fdInv, fdInv.IsDraft));
-            return ct != null
+            if (ct == null)
-                ? await FileContentResultAsync(ct, "application/pdf", filename, inline: true)
+                return await InvoiceIssueResult("Die Rechnungs-PDF konnte aufgrund eines Fehlers nicht erstellt werden.", fdInv.Id);
-                : await InvoiceIssueResult("Die Rechnungs-PDF konnte aufgrund eines Fehlers nicht erstellt werden.", fdInv.Id);
+            // Serve inline for the in-browser viewer, but carry the real DocumentName so the browser's
+            // "download" uses "Rechnung R2026-0121.pdf" instead of the "idoc" endpoint segment. (The
+            // OCORE FileContentResult helper drops the filename under ASP.NET Core, so set it here.)
+            SetInlinePdfFilename(filename);
+            return File(ct, "application/pdf");
         }
         var imgcol = await _pdf.DocToImageCollectionAsync(_invoices.GenerateInvoicePdf(fdInv, fdInv.IsDraft));
         return await JSONAsync(new { id = fdInv.Id, img = imgcol.ImgB64Array, total = imgcol.TotalPages });

Fuchs/Controllers/IntranetController.cs

@@ -35,6 +35,9 @@ public partial class IntranetController : Microsoft.AspNetCore.Mvc.Controller
     private readonly IInvoiceService _invoices;
     private readonly IReminderService _reminders;
     private readonly IEventService _events;
+    private readonly IInvoiceDraftService _invoiceDrafts;
+    private readonly IReminderDraftService _reminderDrafts;
+    private readonly IDraftNotifier _draftNotifier;
     private readonly List<string> _allowedNonAuth = new() { "spwc", "spw" };
     private readonly List<string> _allowedGet = new()
     {
@@ -62,7 +65,10 @@ public partial class IntranetController : Microsoft.AspNetCore.Mvc.Controller
         IReportService reports,
         IInvoiceService invoices,
         IReminderService reminders,
-        IEventService events)
+        IEventService events,
+        IInvoiceDraftService invoiceDrafts,
+        IReminderDraftService reminderDrafts,
+        IDraftNotifier draftNotifier)
     {
         _intranet = intranet;
         _mfr = mfr;
@@ -76,6 +82,9 @@ public partial class IntranetController : Microsoft.AspNetCore.Mvc.Controller
         _invoices = invoices;
         _reminders = reminders;
         _events = events;
+        _invoiceDrafts = invoiceDrafts;
+        _reminderDrafts = reminderDrafts;
+        _draftNotifier = draftNotifier;
     }
 
     /// <summary>Merged query-string + form parameters (form wins) for report processing.</summary>

Fuchs/Docs/Concepts/live-draft-editing.md

@@ -0,0 +1,146 @@
+---
+status: Active
+lastUpdated: 2026-07-10
+applyTo:
+  - "Fuchs/Services/InvoiceDraft*"
+  - "Fuchs/Services/IInvoiceDraft*"
+  - "Fuchs/Services/ReminderDraft*"
+  - "Fuchs/Services/IReminderDraft*"
+  - "Fuchs/code/InvoiceDraftSession.cs"
+  - "Fuchs/code/InvoiceDraftCalculator.cs"
+  - "Fuchs/code/ReminderDraftSession.cs"
+  - "Fuchs/code/ReminderDraftCalculator.cs"
+  - "Fuchs/Notifications/DraftPreviewHub.cs"
+  - "Fuchs/Notifications/*DraftNotifier*"
+  - "Fuchs/Controllers/IntranetController.InvoiceDraft.cs"
+  - "Fuchs/Controllers/IntranetController.ReminderDraft.cs"
+  - "Fuchs/js/intranet/**"
+relatedDecisions:
+  - "0006-backend-authoritative-draft-editing.md"
+  - "0007-targeted-draft-signalr-groups.md"
+---
+
+# Live draft editing (backend-authoritative invoice previews)
+
+## Summary
+While a back-office user edits an invoice draft, the authoritative state is held in
+server memory, not in the browser. The browser posts single edits, the server mutates
+the cached record, recomputes totals/VAT and re-validates, then pushes a "state changed"
+signal so the browser re-fetches and re-renders. This makes the backend the single source
+of truth (server-computed sums, consistency checks, in-place PDF preview, change history,
+explicit discard), reversing the earlier stateless editor. Invoices were the pilot;
+reminders now mirror the same design (see "Reminders" below).
+
+## How it works
+
+```
+Open:     Browser --POST inv/dopen {id | payload}--> server builds InvoiceDraftSession, caches it
+          Browser --SignalR JoinDraft(token)--> joins the draft's group; spinner while loading
+          Browser --POST inv/dstate {token}--> renders admin/new/req + server sums + validation
+
+Edit:     Browser --POST inv/dpatch {token, delta}--> mutate + recompute + validate + version++
+          Server  --SignalR draftReady{token,version}--> Browser re-fetches inv/dstate, re-renders
+
+Preview:  Browser --POST inv/dpreview {token}--> PDF rendered straight from the cache (no upload)
+Save:     Browser --POST inv/dsave {token}--> flush cache->DB (RegisterInvoiceAsync) + EventService toast
+History:  Browser --POST inv/dhistory {token}--> change list -> "Änderungshistorie" dialog
+Discard:  Browser --POST inv/ddiscard {token}--> reload session from DB draft -> draftReady
+Close:    Browser --POST inv/dclose {token}--> session removed (+ LeaveDraft)
+
+Expiry:   Server (timer) --SignalR draftExpiring{token,secondsLeft}--> warn "bitte zwischenspeichern"
+          Server (evict) --SignalR draftClosed{token,reason}--> close the editor with a reason
+```
+
+- **Session** (`InvoiceDraftSession`) is a pure data holder: the editable payload as the
+  exact editor JSON (`admin` / `new` / `req` blocks with `items`), plus server-computed
+  `Sums`, `ValidationMessages`, `History`, `Version`, `Token`, `InvId`, `LastAccessUtc`.
+- **Calculation** (`InvoiceDraftCalculator`, static/pure) ports the former client math:
+  `RecomputeItem` (quantity × price × VAT, the `quantChange` port), `RecomputeTotals`
+  (the `invSumUpdate`/`csms` aggregation + §13b reverse-charge), `RecomputePositions`
+  (numbers every line except heading/free-text lines continuously across the whole invoice —
+  mirroring the editor's `invSumUpdate`, so the editor and the PDF show identical `Pos.` numbers,
+  including after a reorder),
+  and `Validate` (email/address/items/VAT-rate/negative-total checks). Being pure, it is
+  exhaustively unit-tested.
+- **Sanitisation & reorder.** Scalar text deltas (`title`/`email`/`address`/`provisionperiod`/
+  `provisionlocation`) and the section heading (`block.replace`) are stripped of the editor's
+  TinyMCE HTML (`<p>…</p>`, `<br>`) to plain text in `ApplyDelta` (`HtmlToPlain`) — the backend
+  is the single source of truth, so no HTML reaches the DB, the PDF or a reloaded draft. Section
+  drags post a `block.order` delta (`["id",…]`) that reorders `Req`; positions are then
+  renumbered and pushed back via the view state (`applyState`/`applyPositions`). The change
+  history records the **changed field** (e.g. the new heading text), never the whole block JSON.
+  The PDF (`FuchsPdf`) renders a heading row per block (`FdsInvoiceData.InvoiceBlocks`) and shows
+  every position's price (set members are priced like standalone lines; only `setonly` collapses
+  them), so the PDF preview mirrors the online editor.
+- **Orchestration** (`InvoiceDraftEditService`, scoped) opens sessions (from a fresh
+  payload or by reloading a DB draft via `fds__getInvoice`, reshaped like
+  `BuildInvoiceRequestList`), applies deltas (`ApplyDelta`), builds the view-state DTO,
+  flushes to the DB by reusing `IInvoiceService.RegisterInvoiceAsync` (no new persistence
+  path), renders previews from a synthesised registration, and discards by reloading.
+- **Cache** (`InvoiceDraftCache`, singleton) stores sessions by token with an idle sliding
+  TTL; `InvoiceDraftExpiryService` (a `BackgroundService`) warns before, and evicts after,
+  the TTL. TTL/warn-lead are configurable under `Fuchs:DraftEditing`.
+- **Signals** (`DraftPreviewHub` at `/draftpreview` + `IDraftNotifier`) are targeted at the
+  editing browser via a group named after the session token: `draftReady`, `draftExpiring`,
+  `draftClosed`. Business success/failure still flows through `IEventService`/`NotificationHub`.
+- **Frontend** (`$fis.draft` in `fis_main.js`, editor in `fis.inv_shared.js`) opens/joins,
+  posts one delta per change, shows a loading state whenever awaiting a signal, and offers
+  "Änderungen verwerfen" and "Änderungshistorie" menu actions. It no longer computes totals.
+
+## Key files
+- `Fuchs/code/InvoiceDraftSession.cs` — session + `ChangeHistoryEntry` + `InvoiceDraftSums`.
+- `Fuchs/code/InvoiceDraftCalculator.cs` — pure recompute + validate.
+- `Fuchs/Services/InvoiceDraftCache.cs` / `IInvoiceDraftCache.cs` — in-memory store + TTL.
+- `Fuchs/Services/InvoiceDraftEditService.cs` / `IInvoiceDraftService.cs` — orchestration + delta contract.
+- `Fuchs/Services/InvoiceDraftExpiryService.cs` — idle warn/evict monitor.
+- `Fuchs/Notifications/DraftPreviewHub.cs`, `DraftNotifier.cs`, `IDraftNotifier.cs` — targeted signals.
+- `Fuchs/Controllers/IntranetController.InvoiceDraft.cs` — `inv/d*` endpoints.
+- `Fuchs/js/intranet/fis_main.js`, `Fuchs/js/intranet/modules/fis.inv_shared.js` — client.
+
+## Reminders (Zahlungserinnerung)
+
+Reminders mirror the same backend-authoritative model with a reminder-shaped session. A
+reminder chases a single invoiced amount, so the machinery is simpler than an invoice's:
+there are no line-item blocks, VAT grouping or reordering — just recipient fields and the
+amount pair.
+
+- **Endpoints** are `rem/d*` (`dopen`/`dstate`/`dpatch`/`dpreview`/`dsave`/`dhistory`/`dclose`),
+  dispatched from `Do_Process_Reminder`. Finalise + email still runs through the existing
+  `rem/conf` (`HandleReminderConf`), exactly as invoices finalise through `req/sconf`.
+- **Session** (`ReminderDraftSession`) holds the editor's `new` (subject / invoiceaddress /
+  invoiceemail / text / amount / amount_payed / CustomValues) and `rem` (invid / type /
+  invoiceid / invoicedate) blocks, plus server-computed `Sums` (`AmountTotal`, `AmountPayed`,
+  `AmountOpen`). It reuses the shared `ChangeHistoryEntry`; validation uses
+  `ReminderDraftValidationMessage`.
+- **Calculation** (`ReminderDraftCalculator`, static/pure): `AmountOpen = AmountTotal − AmountPayed`,
+  plus email/address/subject/open-amount plausibility checks. Exhaustively unit-tested.
+- **Deltas** (`ReminderDraftDelta`): scalar `email`/`address`/`subject`/`text` (HTML-sanitised via
+  the shared `InvoiceDraftEditService.HtmlToPlain`), the numeric `amount`/`amount_payed`
+  (normalised to an invariant decimal string), and `contact` (→ `CustomValues`).
+- **Orchestration** (`ReminderDraftEditService`, scoped) flushes to the DB by reusing
+  `IReminderService.RegisterReminderAsync`, and renders previews from a synthesised
+  `ReminderRegistration` (including the single-invoice `invoices` row the reminder PDF table
+  renders) so a preview needs no DB round-trip. **Note:** `RegisterReminderAsync` is create-only
+  (there is no `fds__setReminder` update proc), so a re-saved reminder draft does not update the
+  prior DB row — the primary flow (preview → confirm) flushes once immediately before finalising.
+- **Cache/expiry** (`ReminderDraftCache` singleton + `ReminderDraftExpiryService`) mirror the
+  invoice ones and share the same `Fuchs:DraftEditing` TTL config.
+- **Signals** reuse the shared `DraftPreviewHub` + `IDraftNotifier` unchanged — the token-keyed
+  groups serve invoice and reminder drafts alike.
+- **Frontend** (`$inv.rd` in `fis.inv_shared.js`) opens/joins on `rem/dopen`, posts one delta per
+  inline edit and per item-row amount change, renders the open-amount footer + validation from the
+  server state, and previews/finalises through `rem/dpreview` → `rem/dsave` → `rem/conf`. It shares
+  the invoice editor DOM; `$inv.d` and `$inv.rd` each key off their own token, so the shared inline
+  editor safely no-ops for whichever mode is inactive.
+
+### Reminder key files
+- `Fuchs/code/ReminderDraftSession.cs` — session + `ReminderDraftSums` + `ReminderDraftValidationMessage`.
+- `Fuchs/code/ReminderDraftCalculator.cs` — pure open-amount recompute + validate.
+- `Fuchs/Services/ReminderDraftCache.cs` / `IReminderDraftCache.cs` — in-memory store + TTL.
+- `Fuchs/Services/ReminderDraftEditService.cs` / `IReminderDraftService.cs` — orchestration + delta contract.
+- `Fuchs/Services/ReminderDraftExpiryService.cs` — idle warn/evict monitor.
+- `Fuchs/Controllers/IntranetController.ReminderDraft.cs` — `rem/d*` endpoints.
+
+## Related decisions
+- [0006 — Backend-authoritative draft editing](../Decisions/0006-backend-authoritative-draft-editing.md)
+- [0007 — Targeted draft SignalR groups](../Decisions/0007-targeted-draft-signalr-groups.md)

Fuchs/Docs/Decisions/0006-backend-authoritative-draft-editing.md

@@ -0,0 +1,88 @@
+---
+status: Accepted
+date: 2026-07-10
+applyTo:
+  - "Fuchs/Services/InvoiceDraft*"
+  - "Fuchs/Services/IInvoiceDraft*"
+  - "Fuchs/code/InvoiceDraftSession.cs"
+  - "Fuchs/code/InvoiceDraftCalculator.cs"
+  - "Fuchs/Notifications/DraftPreviewHub.cs"
+  - "Fuchs/Notifications/*DraftNotifier*"
+  - "Fuchs/Controllers/IntranetController.InvoiceDraft.cs"
+  - "Fuchs/js/intranet/**"
+supersededBy: ""
+---
+
+# 0006 — Invoice draft editing is backend-authoritative over an in-memory cache
+
+## Context
+The invoice editor was deliberately **stateless**: the browser held the working
+model, computed totals/VAT client-side (`invSumUpdate` in `fis.inv_shared.js`) and
+re-posted the whole `invc` JSON on every preview/save. `EVAL_live_invoice_editing.md`
+(2026) recommended keeping it that way and **against** a server-cached, SignalR-driven
+model, because the real-time/co-editing benefits were weak for a single back-office
+editor.
+
+The product owner has since decided the trade-off differently and prioritised a
+**single source of truth in the backend** with server-computed sums, server-side
+plausibility/consistency checks, in-place PDF preview without re-upload, an automatic
+change history, and an explicit discard. This decision records that reversal and the
+architecture chosen to implement it.
+
+## Decision
+While a user edits an invoice draft, the authoritative state lives **server-side** in
+an in-memory `InvoiceDraftSession` (`Fuchs/code/InvoiceDraftSession.cs`), held by the
+singleton `IInvoiceDraftCache` and orchestrated by the scoped `IInvoiceDraftService`
+(`InvoiceDraftEditService`). The browser is a pure view/input layer.
+
+- **Truth & calculation on the server.** `InvoiceDraftCalculator` is the pure,
+  unit-tested port of the former client-side math (`quantChange` + `invSumUpdate`),
+  including the §13b reverse-charge rule and VAT-per-rate grouping. The browser never
+  computes totals; it renders the server's `sums`.
+- **Commands are ordinary POSTs; signals are SignalR.** The editor posts single edits
+  to `inv/dpatch` (and `dopen`/`dstate`/`dpreview`/`dsave`/`dhistory`/`ddiscard`/`dclose`).
+  The server mutates the session, recomputes, validates, bumps a version, and pings the
+  editing browser (`draftReady`) to re-fetch `inv/dstate`. See
+  [0007](0007-targeted-draft-signalr-groups.md) for the targeted-signal transport.
+- **Cache-only until Zwischenspeichern/Finalise.** Opening builds the session (from a
+  brand-new payload or by reloading a DB draft); edits touch only the cache. `dsave`
+  flushes the session to the DB by reusing the existing
+  `IInvoiceService.RegisterInvoiceAsync` — **no new persistence path** — and reports
+  success/failure through the existing `IEventService` (ADR 0001). Finalise continues
+  through `req/sconf`.
+- **Preview from cache.** `inv/dpreview` renders the draft PDF straight from the session
+  (synthesised registration), with no client upload.
+- **Automatic change history.** Every applied patch appends a `ChangeHistoryEntry`
+  (cache-only, never persisted); `inv/dhistory` exposes it for the "Änderungshistorie"
+  dialog.
+- **Idle lifecycle with user warning.** `InvoiceDraftExpiryService` warns the editing
+  browser before a session's idle TTL lapses (`draftExpiring`) and, on eviction, tells
+  it to close the editor with a reason (`draftClosed`). TTL and warning lead are under
+  `Fuchs:DraftEditing`.
+
+## Consequences
+- The server is now **stateful for in-progress drafts**. This is acceptable for a
+  single-instance deployment; **scale-out requires sticky sessions or a distributed
+  cache/SignalR backplane** — none exist today, so this is a documented limitation, not
+  a silent assumption.
+- New editor interactions must be modelled as a **delta** applied server-side (add a
+  case in `InvoiceDraftEditService.ApplyDelta` + calculator handling), never as a new
+  client-side calculation. Do not reintroduce client-side totals.
+- `FdsInvoiceData` stays a pure data holder; `InvoiceDraftSession` is likewise a data
+  holder, with all logic in the service/calculator (mirrors the existing service split).
+- Reminders (Mahnungen) are intended to follow the identical pattern as a second phase;
+  this decision covers invoices first (the pilot) and applies to the reminder mirror
+  when built.
+- `EVAL_live_invoice_editing.md` and `INVOICE_LIFECYCLE.md` §4/§10 (the "stateless
+  editor" invariant) are superseded by this decision for the draft-editing flow and have
+  been annotated accordingly.
+
+## Alternatives considered
+- **Keep the stateless editor** (the prior recommendation): rejected by the product
+  owner in favour of a backend single source of truth.
+- **Full bidirectional SignalR hub for commands too**: rejected — edits as POSTs reuse
+  the existing controller/auth pattern and avoid a command reconnect/replay protocol; the
+  hub carries only coordination signals.
+- **Write-through to the DB on every edit**: rejected — conflicts with the
+  "Zwischenspeichern = persist the cache" semantics and adds DB load; the cache is the
+  truth until an explicit save/finalise.

Fuchs/Docs/Decisions/0007-targeted-draft-signalr-groups.md

@@ -0,0 +1,59 @@
+---
+status: Accepted
+date: 2026-07-10
+applyTo:
+  - "Fuchs/Notifications/DraftPreviewHub.cs"
+  - "Fuchs/Notifications/IDraftNotifier.cs"
+  - "Fuchs/Notifications/DraftNotifier.cs"
+  - "Fuchs/Program.cs"
+  - "Fuchs/js/intranet/**"
+supersededBy: ""
+---
+
+# 0007 — Draft-editing signals are targeted via a dedicated hub with per-draft groups
+
+## Context
+Backend-authoritative draft editing (ADR 0006) needs to notify **exactly the one
+browser** editing a given draft that its cached state changed, is about to expire, or
+was closed. The existing `NotificationHub` (ADR 0002) deliberately **broadcasts** every
+business toast to all logged-in sessions and explicitly deferred per-user/targeted
+delivery as "a new decision". Draft coordination pings are high-frequency, per-editor,
+and must not spray to every session.
+
+## Decision
+Draft signals use a **dedicated** SignalR hub, `DraftPreviewHub`, mapped at
+`/draftpreview` (separate from `NotificationHub` at `/notifications`). Targeting is by
+**SignalR group named after the draft's session token**:
+
+- The client calls the hub methods `JoinDraft(token)` / `LeaveDraft(token)` to
+  subscribe/unsubscribe its connection to a draft's group. The hub carries **no
+  commands** — only group membership (edits are POSTs; see ADR 0006).
+- The server sends via `IDraftNotifier` (`DraftNotifier`) to `Clients.Group(token)`:
+  `draftReady{token,version}` (re-fetch), `draftExpiring{token,secondsLeft}` (idle
+  warning), `draftClosed{token,reason}` (session evicted/discarded → close the editor).
+- Like `EventService`, delivery failures are logged and swallowed — a missed
+  coordination ping must never fail the underlying operation; the client also re-syncs on
+  reconnect and on its next POST.
+
+Business success/failure messages for draft operations (e.g. "Zwischenstand
+gespeichert") continue to flow through `IEventService`/`NotificationHub`, **not** this
+hub — the two channels stay separate.
+
+## Consequences
+- The session **token doubles as the group name**; it is an opaque GUID and must not
+  encode sensitive data. Any browser that knows a token can join its group, so tokens
+  must be treated as capabilities and only handed to the authenticated editor that opened
+  the draft.
+- Adding a new draft signal means adding a method to `IDraftNotifier` + `DraftNotifier`
+  and a client handler in `$fis.draft` — not overloading the business notification path.
+- ADR 0002 is unchanged: `NotificationHub` stays broadcast-only for toasts. This hub is
+  the answer to its "if per-user targeting becomes necessary, that is a new decision".
+- Multi-instance scale-out needs a SignalR backplane for group delivery — same limitation
+  as ADR 0006.
+
+## Alternatives considered
+- **Reuse `NotificationHub` with groups**: rejected — it would entangle broadcast toasts
+  with targeted, high-frequency editing pings and force ADR 0002's broadcast contract to
+  change. A separate hub keeps the concerns and their decisions independent.
+- **Per-user groups (by account id)**: rejected — a user may open two drafts/tabs;
+  per-draft-token groups target the precise editor and naturally support that.

Fuchs/Docs/EVAL_live_invoice_editing.md

@@ -1,5 +1,17 @@
 # Evaluation — Backend-cached invoice editing over SignalR
 
+> **⚠️ Superseded (2026-07-10).** This note's recommendation (keep the editor
+> stateless; do **not** build the SignalR/server-cached model) was reversed by the
+> product owner. Invoice draft editing is now backend-authoritative over an in-memory
+> cache — see **ADR
+> [`Decisions/0006-backend-authoritative-draft-editing.md`](Decisions/0006-backend-authoritative-draft-editing.md)**,
+> [`Decisions/0007-targeted-draft-signalr-groups.md`](Decisions/0007-targeted-draft-signalr-groups.md)
+> and the concept doc [`Concepts/live-draft-editing.md`](Concepts/live-draft-editing.md).
+> The analysis below is retained for the historical rationale and the risks it flagged
+> (server-held state, scaling/backplane, reconnect) — which the new design addresses or
+> accepts explicitly as documented limitations.
+
+
 **Idea (as proposed):** hold invoices that users are editing in a **server-side
 cache**, keep a **SignalR / WebSocket** connection open, apply each front-end
 change **in the backend**, and **push the recomputed state back** to the browser.

Fuchs/Docs/INVOICE_LIFECYCLE.md

@@ -337,9 +337,18 @@ flowchart TD
 
 ## 10. Key invariants worth remembering
 
-- **Stateless editor**: every preview/save/finalise call re-posts the full
+> **⚠️ Updated (2026-07-10):** the "stateless editor" invariant below describes the
-  `invc` JSON; the server never holds a partial invoice in memory or session
+> **legacy** draft-editing flow. Invoice draft editing is being moved to a
-  between requests (see `EVAL_live_invoice_editing.md`).
+> **backend-authoritative** model where the server holds the draft in an in-memory
+> cache (the single source of truth), the browser posts single edits and re-fetches on
+> a SignalR signal, and totals are computed server-side. See ADR
+> [`Decisions/0006-backend-authoritative-draft-editing.md`](Decisions/0006-backend-authoritative-draft-editing.md)
+> and [`Concepts/live-draft-editing.md`](Concepts/live-draft-editing.md). Finalise/email
+> (§5–§6) are unchanged. The remaining invariants below still hold.
+
+- **Stateless editor** *(legacy — see the note above; superseded by ADR 0006)*: every
+  preview/save/finalise call re-posts the full `invc` JSON; the server never holds a
+  partial invoice in memory or session between requests (see `EVAL_live_invoice_editing.md`).
 - **Totals come from the registration, not the rendered lines**: `sms.ttn`
   /`sms.ttb` (posted) become `InvoiceBalance`/`InvoiceBalance_net`; display
   mode (set pricing) never changes what the customer owes.

Fuchs/Notifications/DomainEvent.cs

@@ -12,6 +12,7 @@ public enum DomainEventType
     InvoiceFileCreationFailed,
     InvoiceSendFailed,
     ReminderDraftCreated,
+    ReminderDraftUpdated,
     ReminderFileCreated,
     ReminderSentToCustomer,
     ReminderResentToCustomer,

Fuchs/Notifications/DraftNotifier.cs

@@ -0,0 +1,45 @@
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging;
+
+namespace Fuchs.Notifications;
+
+/// <summary>
+/// <see cref="IDraftNotifier"/> over the <see cref="DraftPreviewHub"/>. Sends to the
+/// SignalR group named after the draft token so only the editing browser is notified.
+/// Like <see cref="EventService.PublishAsync"/>, delivery failures are logged and
+/// swallowed — a missed coordination ping must never fail the underlying operation
+/// (the client also re-syncs on reconnect and on its next POST).
+/// </summary>
+public sealed class DraftNotifier : IDraftNotifier
+{
+    private readonly IHubContext<DraftPreviewHub> _hub;
+    private readonly ILogger<DraftNotifier> _logger;
+
+    public DraftNotifier(IHubContext<DraftPreviewHub> hub, ILogger<DraftNotifier> logger)
+    {
+        _hub = hub;
+        _logger = logger;
+    }
+
+    public Task SignalDraftReadyAsync(string token, int version, CancellationToken cancellationToken = default) =>
+        SendAsync(token, "draftReady", new { token, version }, cancellationToken);
+
+    public Task SignalExpiringAsync(string token, int secondsLeft, CancellationToken cancellationToken = default) =>
+        SendAsync(token, "draftExpiring", new { token, secondsLeft }, cancellationToken);
+
+    public Task SignalClosedAsync(string token, string reason, CancellationToken cancellationToken = default) =>
+        SendAsync(token, "draftClosed", new { token, reason }, cancellationToken);
+
+    private async Task SendAsync(string token, string method, object payload, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrEmpty(token)) return;
+        try
+        {
+            await _hub.Clients.Group(token).SendAsync(method, payload, cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Draft signal {Method} failed for token {Token}", method, token);
+        }
+    }
+}

Fuchs/Notifications/DraftPreviewHub.cs

@@ -0,0 +1,31 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+
+namespace Fuchs.Notifications;
+
+/// <summary>
+/// SignalR hub for live invoice/reminder draft editing (see ADR 0006 / 0007).
+///
+/// Deliberately separate from <see cref="NotificationHub"/>: that hub broadcasts
+/// business toasts to <b>all</b> logged-in sessions (ADR 0002), whereas draft
+/// signals must be <b>targeted</b> at the one browser editing a given draft.
+/// Targeting is done with a SignalR group named after the draft's session token —
+/// each editor calls <see cref="JoinDraft"/> after opening a draft.
+///
+/// The hub carries no commands: edits, saves and discards travel as ordinary POSTs
+/// (see ADR 0006). The hub only manages group membership and delivers the server's
+/// <c>draftReady</c> / <c>draftExpiring</c> / <c>draftClosed</c> signals.
+/// </summary>
+[Authorize]
+public sealed class DraftPreviewHub : Hub
+{
+    /// <summary>Subscribes this connection to a draft's signal group.</summary>
+    public Task JoinDraft(string token) =>
+        string.IsNullOrEmpty(token) ? Task.CompletedTask
+            : Groups.AddToGroupAsync(Context.ConnectionId, token);
+
+    /// <summary>Unsubscribes this connection from a draft's signal group.</summary>
+    public Task LeaveDraft(string token) =>
+        string.IsNullOrEmpty(token) ? Task.CompletedTask
+            : Groups.RemoveFromGroupAsync(Context.ConnectionId, token);
+}

Fuchs/Notifications/EventService.cs

@@ -76,6 +76,12 @@ public sealed class EventService : IEventService
     public Task ReminderDraftCreatedAsync(FdsReminderData reminder, string userAccountId)
         => PublishAsync(new DomainEvent(DomainEventType.ReminderDraftCreated, userAccountId, "Mahnentwurf", ReminderContext(reminder)));
 
+    public Task ReminderDraftRegisteredAsync(FdsReminderData reminder, bool changed, string userAccountId)
+    {
+        var type = changed ? DomainEventType.ReminderDraftUpdated : DomainEventType.ReminderDraftCreated;
+        return PublishAsync(new DomainEvent(type, userAccountId, "Mahnentwurf", ReminderContext(reminder)));
+    }
+
     public Task ReminderFileCreatedAsync(FdsReminderData reminder, string fileName, string userAccountId)
     {
         var ctx = ReminderContext(reminder);
@@ -176,6 +182,8 @@ public sealed class EventService : IEventService
                 Ctx(domainEvent, "message"),
             DomainEventType.ReminderDraftCreated =>
                 $"Mahnentwurf {Ctx(domainEvent, "title")} wurde erstellt.",
+            DomainEventType.ReminderDraftUpdated =>
+                $"Mahnentwurf {Ctx(domainEvent, "title")} wurde aktualisiert.",
             DomainEventType.ReminderFileCreated =>
                 $"Mahndatei {Ctx(domainEvent, "fileName")} wurde erstellt.",
             DomainEventType.ReminderSentToCustomer =>

Fuchs/Notifications/IDraftNotifier.cs

@@ -0,0 +1,20 @@
+namespace Fuchs.Notifications;
+
+/// <summary>
+/// Sends <b>system-internal</b> draft-editing signals to the one browser editing a
+/// given draft, over the <see cref="DraftPreviewHub"/> group keyed by session token
+/// (see ADR 0006 / 0007). These are coordination pings, not business notifications:
+/// user-facing success/failure messages (e.g. "Zwischenstand gespeichert") still go
+/// through <see cref="IEventService"/> / <see cref="NotificationHub"/>.
+/// </summary>
+public interface IDraftNotifier
+{
+    /// <summary>The cached draft reached a new <paramref name="version"/> — the client should re-fetch its state.</summary>
+    Task SignalDraftReadyAsync(string token, int version, CancellationToken cancellationToken = default);
+
+    /// <summary>The draft is about to expire in <paramref name="secondsLeft"/>s unless saved — warn the user.</summary>
+    Task SignalExpiringAsync(string token, int secondsLeft, CancellationToken cancellationToken = default);
+
+    /// <summary>The draft session was removed (evicted/expired/discarded) — the client must close the editor and show why.</summary>
+    Task SignalClosedAsync(string token, string reason, CancellationToken cancellationToken = default);
+}

Fuchs/Notifications/IEventService.cs

@@ -13,6 +13,7 @@ public interface IEventService
     Task InvoiceIssueAsync(string message, string userAccountId, string invoiceId = "");
 
     Task ReminderDraftCreatedAsync(FdsReminderData reminder, string userAccountId);
+    Task ReminderDraftRegisteredAsync(FdsReminderData reminder, bool changed, string userAccountId);
     Task ReminderFileCreatedAsync(FdsReminderData reminder, string fileName, string userAccountId);
     Task ReminderSentToCustomerAsync(FdsReminderData reminder, string email, string userAccountId, bool resent = false);
     Task ReminderMarkedSentAsync(string reminderId, string reminderTitle, string userAccountId);

Fuchs/Program.cs

@@ -110,6 +110,20 @@ public class Program
         builder.Services.AddScoped<IReminderService, ReminderService>();
         builder.Services.AddScoped<IEventService, EventService>();
 
+        // Live, backend-authoritative invoice draft editing (ADR 0006): an in-memory
+        // draft cache (singleton), the scoped edit orchestrator, a targeted SignalR
+        // notifier over the dedicated DraftPreviewHub, and the idle-expiry monitor.
+        builder.Services.AddSingleton<IInvoiceDraftCache, InvoiceDraftCache>();
+        builder.Services.AddSingleton<IDraftNotifier, DraftNotifier>();
+        builder.Services.AddScoped<IInvoiceDraftService, InvoiceDraftEditService>();
+        builder.Services.AddHostedService<InvoiceDraftExpiryService>();
+
+        // Live, backend-authoritative reminder draft editing (ADR 0006) — the reminder
+        // mirror of the invoice draft services above, sharing the DraftPreviewHub/notifier.
+        builder.Services.AddSingleton<IReminderDraftCache, ReminderDraftCache>();
+        builder.Services.AddScoped<IReminderDraftService, ReminderDraftEditService>();
+        builder.Services.AddHostedService<ReminderDraftExpiryService>();
+
         // Secondary archive: invoice/reminder PDFs additionally stored in Azure Blob Storage.
         // Disabled by default (Fuchs:AzureStorage:Enabled) — see AzureBlobStorageService.
         builder.Services.Configure<AzureBlobStorageSettings>(builder.Configuration.GetSection("Fuchs:AzureStorage"));
@@ -184,6 +198,7 @@ public class Program
         app.UseAuthentication();
         app.UseAuthorization();
         app.MapHub<NotificationHub>("/notifications");
+        app.MapHub<DraftPreviewHub>("/draftpreview");
 
         // Intranet routes (root-level — this IS the website)
         app.MapControllerRoute(

Fuchs/Services/IInvoiceDraftCache.cs

@@ -0,0 +1,26 @@
+using Fuchs.intranet;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// In-memory store of live invoice draft editing sessions (see ADR 0006).
+/// Singleton, single-instance only — scale-out would need a distributed cache /
+/// sticky sessions (documented limitation). Keyed by the session token.
+/// </summary>
+public interface IInvoiceDraftCache
+{
+    /// <summary>Stores (or replaces) a session under its token.</summary>
+    void Set(InvoiceDraftSession session);
+
+    /// <summary>Returns the session for the token, or null if absent/evicted. Touches <c>LastAccessUtc</c> on hit.</summary>
+    InvoiceDraftSession? Get(string token);
+
+    /// <summary>Removes the session (explicit close/discard/finalise). Returns the removed session, if any.</summary>
+    InvoiceDraftSession? Remove(string token);
+
+    /// <summary>Snapshot of all live sessions — used by the expiry monitor. Does not touch access time.</summary>
+    IReadOnlyList<InvoiceDraftSession> Snapshot();
+
+    /// <summary>The configured idle time-to-live before a session is eligible for eviction.</summary>
+    TimeSpan IdleTtl { get; }
+}

Fuchs/Services/IInvoiceDraftService.cs

@@ -0,0 +1,75 @@
+using Fuchs.intranet;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Orchestrates a live, backend-authoritative invoice draft editing session
+/// (ADR 0006). Owns the lifecycle around an <see cref="InvoiceDraftSession"/>:
+/// open (seed the cache), apply single edits, build the view state, render a PDF
+/// preview from the cache, flush to the DB ("Zwischenspeichern") and expose the
+/// change history. All totals/VAT are aggregated by <see cref="InvoiceDraftCalculator"/>
+/// — the browser never sums.
+///
+/// Reload/discard is handled by the client (re-fetch the DB draft via the existing
+/// <c>inv/get</c> render path and re-seed), so there is no server-side DB reshaping here.
+/// </summary>
+public interface IInvoiceDraftService
+{
+    /// <summary>
+    /// Seeds a new cache session from the editor's assembled payload
+    /// (<c>admin</c> / <c>new</c> / <c>req</c> blocks, each block carrying the editor's
+    /// <c>itm</c>/<c>items</c> line arrays). Computes totals + validation and returns the
+    /// session (with its fresh token/version). An <c>invid</c> in the payload marks it as
+    /// an update of an existing DB draft.
+    /// </summary>
+    InvoiceDraftSession OpenFromPayload(JObject payload, string userAccountId);
+
+    /// <summary>Returns the cached session for the token (touching its TTL), or null if absent/expired.</summary>
+    InvoiceDraftSession? Get(string token);
+
+    /// <summary>
+    /// Applies one editor change to the cached session: mutates the payload, re-aggregates
+    /// totals, re-validates, appends a history entry and bumps the version. Returns the
+    /// mutated session, or null if the token is unknown.
+    /// </summary>
+    InvoiceDraftSession? ApplyPatch(string token, InvoiceDraftDelta delta);
+
+    /// <summary>Builds the JSON view-state DTO the frontend renders (payload + server sums + validation + version).</summary>
+    object BuildState(InvoiceDraftSession session);
+
+    /// <summary>The draft's change history for the "Änderungshistorie" dialog (empty if the token is unknown).</summary>
+    IReadOnlyList<ChangeHistoryEntry> GetHistory(string token);
+
+    /// <summary>
+    /// Persists the cached session to the DB via the existing invoice registration path
+    /// ("Zwischenspeichern"). Sets <see cref="InvoiceDraftSession.InvId"/> on success.
+    /// Returns the registered invoice data (for the success event), or null if the token is unknown.
+    /// </summary>
+    Task<FdsInvoiceData?> FlushToDbAsync(string token, string userAccountId, DatabaseSecurity dbSec);
+
+    /// <summary>Renders a draft PDF straight from the cached session (no client upload). Null if token unknown.</summary>
+    Document? RenderPreview(string token);
+
+    /// <summary>Removes the session from the cache (explicit close/discard/finalise). Returns true if one was present.</summary>
+    bool Close(string token);
+}
+
+/// <summary>
+/// A single editor change posted to <c>inv/dpatch</c>. <see cref="Target"/> names the
+/// field/operation (e.g. "email", "p13b", "block.replace"); <see cref="Ref"/> is the block
+/// id it applies to (when relevant); <see cref="Value"/> is the new value (a scalar for
+/// fields, or a full block object for <c>block.replace</c>).
+/// </summary>
+public sealed class InvoiceDraftDelta
+{
+    public string Target { get; set; } = "";
+    public string Ref { get; set; } = "";
+    public JToken? Value { get; set; }
+
+    /// <summary>The new value as a string (empty when null), for history and simple field assignments.</summary>
+    public string ValueString =>
+        Value == null || Value.Type == JTokenType.Null ? "" : Value.Type == JTokenType.String ? Value.Value<string>() ?? "" : Value.ToString();
+}

Fuchs/Services/IReminderDraftCache.cs

@@ -0,0 +1,27 @@
+using Fuchs.intranet;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// In-memory store of live reminder draft editing sessions (see ADR 0006, mirroring
+/// <see cref="IInvoiceDraftCache"/>). Singleton, single-instance only — scale-out would
+/// need a distributed cache / sticky sessions (documented limitation). Keyed by the
+/// session token.
+/// </summary>
+public interface IReminderDraftCache
+{
+    /// <summary>Stores (or replaces) a session under its token.</summary>
+    void Set(ReminderDraftSession session);
+
+    /// <summary>Returns the session for the token, or null if absent/evicted. Touches <c>LastAccessUtc</c> on hit.</summary>
+    ReminderDraftSession? Get(string token);
+
+    /// <summary>Removes the session (explicit close/discard/finalise). Returns the removed session, if any.</summary>
+    ReminderDraftSession? Remove(string token);
+
+    /// <summary>Snapshot of all live sessions — used by the expiry monitor. Does not touch access time.</summary>
+    IReadOnlyList<ReminderDraftSession> Snapshot();
+
+    /// <summary>The configured idle time-to-live before a session is eligible for eviction.</summary>
+    TimeSpan IdleTtl { get; }
+}

Fuchs/Services/IReminderDraftService.cs

@@ -0,0 +1,73 @@
+using Fuchs.intranet;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Orchestrates a live, backend-authoritative reminder draft editing session (ADR 0006,
+/// mirroring <see cref="IInvoiceDraftService"/>). Owns the lifecycle around a
+/// <see cref="ReminderDraftSession"/>: open (seed the cache), apply single edits, build the
+/// view state, render a PDF preview from the cache, flush to the DB ("Zwischenspeichern")
+/// and expose the change history. The open amount is aggregated by
+/// <see cref="ReminderDraftCalculator"/> — the browser never sums.
+///
+/// Reload/discard is handled by the client (re-fetch the DB draft / prep data via the
+/// existing <c>rem/get</c> path and re-seed), so there is no server-side DB reshaping here.
+/// </summary>
+public interface IReminderDraftService
+{
+    /// <summary>
+    /// Seeds a new cache session from the editor's assembled payload (<c>new</c> / <c>rem</c>
+    /// blocks). Computes the open amount + validation and returns the session (with its fresh
+    /// token/version). A <c>remid</c> in the payload marks it as an update of an existing DB draft.
+    /// </summary>
+    ReminderDraftSession OpenFromPayload(JObject payload, string userAccountId);
+
+    /// <summary>Returns the cached session for the token (touching its TTL), or null if absent/expired.</summary>
+    ReminderDraftSession? Get(string token);
+
+    /// <summary>
+    /// Applies one editor change to the cached session: mutates the payload, re-aggregates the
+    /// open amount, re-validates, appends a history entry and bumps the version. Returns the
+    /// mutated session, or null if the token is unknown.
+    /// </summary>
+    ReminderDraftSession? ApplyPatch(string token, ReminderDraftDelta delta);
+
+    /// <summary>Builds the JSON view-state DTO the frontend renders (payload + server sums + validation + version).</summary>
+    object BuildState(ReminderDraftSession session);
+
+    /// <summary>The draft's change history for the "Änderungshistorie" dialog (empty if the token is unknown).</summary>
+    IReadOnlyList<ChangeHistoryEntry> GetHistory(string token);
+
+    /// <summary>
+    /// Persists the cached session to the DB via the existing reminder registration path
+    /// ("Zwischenspeichern"). Sets <see cref="ReminderDraftSession.RemId"/> on success.
+    /// Returns the registered reminder data (for the success event), or null if the token is unknown.
+    /// </summary>
+    Task<FdsReminderData?> FlushToDbAsync(string token, string userAccountId, DatabaseSecurity dbSec);
+
+    /// <summary>Renders a draft PDF straight from the cached session (no client upload). Null if token unknown.</summary>
+    Document? RenderPreview(string token);
+
+    /// <summary>Removes the session from the cache (explicit close/discard/finalise). Returns true if one was present.</summary>
+    bool Close(string token);
+}
+
+/// <summary>
+/// A single editor change posted to <c>rem/dpatch</c>. <see cref="Target"/> names the
+/// field/operation (e.g. "email", "subject", "amount"); <see cref="Ref"/> is reserved for
+/// future per-item edits; <see cref="Value"/> is the new value (a scalar for fields, or a
+/// small object for <c>contact</c>).
+/// </summary>
+public sealed class ReminderDraftDelta
+{
+    public string Target { get; set; } = "";
+    public string Ref { get; set; } = "";
+    public JToken? Value { get; set; }
+
+    /// <summary>The new value as a string (empty when null), for history and simple field assignments.</summary>
+    public string ValueString =>
+        Value == null || Value.Type == JTokenType.Null ? "" : Value.Type == JTokenType.String ? Value.Value<string>() ?? "" : Value.ToString();
+}

Fuchs/Services/InvoiceDraftCache.cs

@@ -0,0 +1,60 @@
+using System.Collections.Concurrent;
+using Fuchs.intranet;
+using Microsoft.Extensions.Configuration;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Single-instance, in-memory implementation of <see cref="IInvoiceDraftCache"/>
+/// backed by a <see cref="ConcurrentDictionary{TKey,TValue}"/> keyed by session
+/// token. A plain dictionary (rather than <c>IMemoryCache</c>) is used on purpose:
+/// the <see cref="InvoiceDraftExpiryService"/> needs to enumerate sessions and warn
+/// the user <b>before</b> eviction, which opaque cache-entry expiry does not allow.
+///
+/// Idle TTL and the pre-expiry warning lead time are configurable under
+/// <c>Fuchs:DraftEditing</c> (<c>IdleMinutes</c> / <c>ExpiryWarnMinutes</c>).
+/// </summary>
+public sealed class InvoiceDraftCache : IInvoiceDraftCache
+{
+    private readonly ConcurrentDictionary<string, InvoiceDraftSession> _sessions = new(StringComparer.Ordinal);
+
+    public TimeSpan IdleTtl { get; }
+    /// <summary>How long before the idle TTL a warning is emitted to the user.</summary>
+    public TimeSpan ExpiryWarnLead { get; }
+
+    public InvoiceDraftCache(IConfiguration configuration)
+    {
+        int idleMinutes = configuration.GetValue("Fuchs:DraftEditing:IdleMinutes", 30);
+        int warnMinutes = configuration.GetValue("Fuchs:DraftEditing:ExpiryWarnMinutes", 5);
+        IdleTtl        = TimeSpan.FromMinutes(Math.Max(1, idleMinutes));
+        ExpiryWarnLead = TimeSpan.FromMinutes(Math.Clamp(warnMinutes, 1, Math.Max(1, idleMinutes - 1)));
+    }
+
+    public void Set(InvoiceDraftSession session)
+    {
+        if (string.IsNullOrEmpty(session.Token)) throw new ArgumentException("Session has no token.", nameof(session));
+        session.Touch();
+        _sessions[session.Token] = session;
+    }
+
+    public InvoiceDraftSession? Get(string token)
+    {
+        if (string.IsNullOrEmpty(token)) return null;
+        if (_sessions.TryGetValue(token, out var s))
+        {
+            s.Touch();
+            // A touch resets the idle window, so a fresh warning is due next time it lapses.
+            s.ExpiryWarningSent = false;
+            return s;
+        }
+        return null;
+    }
+
+    public InvoiceDraftSession? Remove(string token)
+    {
+        if (string.IsNullOrEmpty(token)) return null;
+        return _sessions.TryRemove(token, out var s) ? s : null;
+    }
+
+    public IReadOnlyList<InvoiceDraftSession> Snapshot() => _sessions.Values.ToList();
+}

Fuchs/Services/InvoiceDraftEditService.cs

@@ -0,0 +1,439 @@
+using System.Globalization;
+using System.Text.RegularExpressions;
+using Fuchs.intranet;
+using Microsoft.Extensions.Logging;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+using static OCORE.commons;
+using static OCORE.OCORE_dictionaries;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Backend-authoritative invoice draft editing (ADR 0006). Holds the truth in an
+/// <see cref="InvoiceDraftSession"/> (via <see cref="IInvoiceDraftCache"/>), applies
+/// single edits, aggregates totals with <see cref="InvoiceDraftCalculator"/>, renders
+/// previews and flushes to the DB by reusing the existing <see cref="IInvoiceService"/>
+/// registration path — no new persistence. The session stores the editor's own block
+/// shape (<c>itm</c>/<c>items</c> line arrays), which the PDF/persistence already consume,
+/// so nothing is re-shaped server-side.
+/// </summary>
+public sealed class InvoiceDraftEditService : IInvoiceDraftService
+{
+    private readonly IInvoiceDraftCache _cache;
+    private readonly IInvoiceService _invoices;
+    private readonly ILogger<InvoiceDraftEditService> _logger;
+
+    public InvoiceDraftEditService(IInvoiceDraftCache cache, IInvoiceService invoices,
+        ILogger<InvoiceDraftEditService> logger)
+    {
+        _cache = cache;
+        _invoices = invoices;
+        _logger = logger;
+    }
+
+    // ── Open ─────────────────────────────────────────────────────────────────
+    public InvoiceDraftSession OpenFromPayload(JObject payload, string userAccountId)
+    {
+        var session = new InvoiceDraftSession
+        {
+            Token = NewToken(),
+            UserAccountId = userAccountId,
+            InvId = payload["invid"]?.Value<string>() ?? payload["id"]?.Value<string>() ?? ""
+        };
+        session.Admin = payload["admin"] as JObject ?? new JObject();
+        session.New   = payload["new"]   as JObject ?? new JObject();
+        session.Req   = payload["req"]   as JArray  ?? new JArray();
+        Refresh(session);
+        _cache.Set(session);
+        _logger.LogInformation("Draft session {Token} opened from payload (invId={InvId}, user={User})",
+            session.Token, session.InvId, userAccountId);
+        return session;
+    }
+
+    public InvoiceDraftSession? Get(string token) => _cache.Get(token);
+
+    // ── Patch ──────────────────────────────────────────────────────────────────
+    public InvoiceDraftSession? ApplyPatch(string token, InvoiceDraftDelta delta)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+
+        string oldValue = "", newValue = "";
+        bool mutated = ApplyDelta(session, delta, ref oldValue, ref newValue);
+        if (!mutated)
+        {
+            _logger.LogDebug("Draft {Token}: no-op patch target={Target} ref={Ref}", token, delta.Target, delta.Ref);
+            return session;
+        }
+
+        Refresh(session);
+        session.Version++;
+        session.History.Add(new ChangeHistoryEntry
+        {
+            UserAccountId = session.UserAccountId,
+            Target = delta.Target,
+            Ref = delta.Ref,
+            OldValue = oldValue,
+            NewValue = newValue,
+            Version = session.Version
+        });
+        _cache.Set(session);
+        return session;
+    }
+
+    /// <summary>
+    /// Applies one delta to the payload; returns whether anything changed and captures the prior
+    /// and new value for the change history. Scalar text fields and the section heading are
+    /// sanitised from the editor's HTML (TinyMCE wraps inline edits in <c>&lt;p&gt;…&lt;/p&gt;</c>)
+    /// to plain text here — the backend is the single source of truth (ADR 0006), so no HTML ever
+    /// reaches the DB, the PDF or a reloaded draft, regardless of which UI path produced it.
+    /// </summary>
+    private static bool ApplyDelta(InvoiceDraftSession s, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        switch (d.Target)
+        {
+            case "email":             return SetNewText(s, "invoiceemail", d, ref oldValue, ref newValue);
+            case "address":           return SetNewText(s, "invoiceaddress", d, ref oldValue, ref newValue);
+            case "title":             return SetNewText(s, "invoicetitle", d, ref oldValue, ref newValue);
+            case "provisionperiod":   return SetNewText(s, "provisionperiod", d, ref oldValue, ref newValue);
+            case "provisionlocation":
+                oldValue = Str(s.New["provisionlocation"]);
+                newValue = HtmlToPlain(d.ValueString);
+                s.New["provisionlocation"] = newValue;
+                s.New["loc"] = newValue;   // editor mirrors both
+                return true;
+            case "contact":           return SetContact(s, d, ref oldValue, ref newValue);
+            case "setmode":           return SetAdmin(s, "setmode", d, ref oldValue, ref newValue);
+            case "p13b":
+                oldValue = Str(s.Admin["p13b"]);
+                bool p13b = d.Value != null && d.Value.Type != JTokenType.Null
+                    ? AsBool(d.Value) : !AsBool(s.Admin["p13b"]);   // toggle when no explicit value
+                s.Admin["p13b"] = p13b;
+                newValue = p13b ? "§13b" : "";
+                return true;
+            case "block.replace":     return ReplaceBlock(s, d, ref oldValue, ref newValue);
+            case "block.remove":      return RemoveBlock(s, d, ref oldValue, ref newValue);
+            case "block.order":       return ReorderBlocks(s, d, ref oldValue, ref newValue);
+            default:                  return false;
+        }
+    }
+
+    private static bool SetNewText(InvoiceDraftSession s, string key, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        oldValue = Str(s.New[key]);
+        newValue = HtmlToPlain(d.ValueString);
+        s.New[key] = newValue;
+        return true;
+    }
+
+    private static bool SetAdmin(InvoiceDraftSession s, string key, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        oldValue = Str(s.Admin[key]);
+        newValue = d.ValueString;
+        s.Admin[key] = newValue;
+        return true;
+    }
+
+    private static bool SetContact(InvoiceDraftSession s, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        JObject prev = TryParseObject(Str(s.New["CustomValues"]));
+        oldValue = ContactLabel(Str(prev["contactName"]), Str(prev["contactEmail"]));
+        JObject cvo = (JObject)prev.DeepClone();
+        if (d.Value is JObject vo)
+        {
+            cvo["contactName"]  = vo["name"] ?? vo["contactName"] ?? "";
+            cvo["contactEmail"] = vo["email"] ?? vo["contactEmail"] ?? "";
+        }
+        s.New["CustomValues"] = cvo.ToString(Newtonsoft.Json.Formatting.None);
+        newValue = ContactLabel(Str(cvo["contactName"]), Str(cvo["contactEmail"]));
+        return true;
+    }
+
+    private static string ContactLabel(string name, string email) =>
+        string.IsNullOrEmpty(name) ? email : string.IsNullOrEmpty(email) ? name : $"{name} <{email}>";
+
+    /// <summary>Replaces (or inserts) a whole block — the editor re-emits an edited block's line arrays as one delta.</summary>
+    private static bool ReplaceBlock(InvoiceDraftSession s, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        if (d.Value is not JObject nb) return false;
+        SanitizeBlockText(nb);
+        string bid = !string.IsNullOrEmpty(d.Ref) ? d.Ref : Str(nb["Id"]);
+        var existing = FindBlock(s, bid);
+        if (existing != null)
+        {
+            oldValue = Str(existing["text"]);
+            existing.Replace(nb);
+        }
+        else
+        {
+            oldValue = "";
+            s.Req.Add(nb);
+        }
+        newValue = Str(nb["text"]);   // the section heading — never the whole block JSON
+        return true;
+    }
+
+    private static bool RemoveBlock(InvoiceDraftSession s, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        var block = FindBlock(s, d.Ref);
+        if (block == null) return false;
+        oldValue = Str(block["text"]);
+        newValue = "";
+        block.Remove();
+        return true;
+    }
+
+    /// <summary>
+    /// Reorders the service-request blocks to the id sequence the editor posts after a section
+    /// drag (<c>Value</c> = ["id",…]). Named ids move into the given order; any not named are kept
+    /// in their current relative order at the end. Totals are unaffected; item position numbers
+    /// are renumbered by <see cref="Refresh"/> and pushed back to the browser via the view state.
+    /// </summary>
+    private static bool ReorderBlocks(InvoiceDraftSession s, InvoiceDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        if (d.Value is not JArray order) return false;
+        var current = s.Req.OfType<JObject>().ToList();
+        oldValue = string.Join(",", current.Select(b => Str(b["Id"])));
+
+        var byId = current.ToDictionary(b => Str(b["Id"]), b => b);
+        var ordered = new List<JObject>();
+        var seen = new HashSet<string>();
+        foreach (var idTok in order)
+        {
+            string id = Str(idTok);
+            if (byId.TryGetValue(id, out var blk) && seen.Add(id)) ordered.Add(blk);
+        }
+        foreach (var b in current)   // append blocks the order list didn't mention, in place
+            if (seen.Add(Str(b["Id"]))) ordered.Add(b);
+
+        newValue = string.Join(",", ordered.Select(b => Str(b["Id"])));
+        if (oldValue == newValue) return false;   // no-op reorder
+
+        s.Req.Clear();
+        foreach (var b in ordered) s.Req.Add(b);
+        return true;
+    }
+
+    /// <summary>Strips the editor's HTML from a block's heading (<c>text</c>/<c>nme</c>) before it is cached.</summary>
+    private static void SanitizeBlockText(JObject block)
+    {
+        if (block["text"] != null) block["text"] = HtmlToPlain(Str(block["text"]));
+        if (block["nme"]  != null) block["nme"]  = HtmlToPlain(Str(block["nme"]));
+    }
+
+    // ── View state / history ────────────────────────────────────────────────
+    public object BuildState(InvoiceDraftSession session)
+    {
+        session.Touch();
+        return new
+        {
+            token   = session.Token,
+            version = session.Version,
+            invid   = session.InvId,
+            isDraft = session.IsDraft,
+            admin   = session.Admin,
+            @new    = session.New,
+            req     = session.Req,
+            sums    = new
+            {
+                total_net   = session.Sums.TotalNet,
+                total_gross = session.Sums.TotalGross,
+                total_vat   = session.Sums.TotalVat,
+                service_net = session.Sums.ServiceNet,
+                service_vat = session.Sums.ServiceVat,
+                vat         = session.Sums.VatByRate,
+                block_net   = session.Sums.NetByBlock
+            },
+            validation = session.ValidationMessages.Select(v => new { field = v.Field, severity = v.Severity, message = v.Message }),
+            historyCount = session.History.Count
+        };
+    }
+
+    public IReadOnlyList<ChangeHistoryEntry> GetHistory(string token) =>
+        _cache.Get(token)?.History ?? (IReadOnlyList<ChangeHistoryEntry>)Array.Empty<ChangeHistoryEntry>();
+
+    // ── Flush / preview ────────────────────────────────────────────────────────
+    public async Task<FdsInvoiceData?> FlushToDbAsync(string token, string userAccountId, DatabaseSecurity dbSec)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+
+        var fds = BuildFdsData(session);
+        bool change = !string.IsNullOrEmpty(session.InvId);
+        var reg = await _invoices.RegisterInvoiceAsync(fds, change, session.InvId, userAccountId, dbSec);
+        if (!string.IsNullOrEmpty(reg.Id))
+        {
+            session.InvId = reg.Id;
+            _cache.Set(session);
+            _logger.LogInformation("Draft {Token} flushed to DB invoice {InvId} (change={Change}, user={User})",
+                token, reg.Id, change, userAccountId);
+        }
+        return reg;
+    }
+
+    public Document? RenderPreview(string token)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+        var fds = BuildFdsData(session);
+        fds.InvoiceRegistration = SynthesizeRegistration(session);
+        fds.IsDraft = true;
+        return _invoices.GenerateInvoicePdf(fds, draft: true);
+    }
+
+    public bool Close(string token) => _cache.Remove(token) != null;
+
+    // ── Internals ──────────────────────────────────────────────────────────────
+    private static void Refresh(InvoiceDraftSession session)
+    {
+        InvoiceDraftCalculator.RecomputeTotals(session);
+        InvoiceDraftCalculator.RecomputePositions(session);
+        InvoiceDraftCalculator.Validate(session);
+    }
+
+    private static string NewToken() => Guid.NewGuid().ToString("N");
+
+    private static JObject? FindBlock(InvoiceDraftSession s, string blockId)
+    {
+        foreach (var b in s.Req)
+            if (b is JObject bo && Str(bo["Id"]) == blockId) return bo;
+        return null;
+    }
+
+    /// <summary>
+    /// Builds the <see cref="FdsInvoiceData"/> from the session — the server-side equivalent
+    /// of <c>invcPayload</c>. The session already holds the editor's <c>req</c> block shape
+    /// (<c>itm</c>/<c>items</c> line arrays) that registration and the PDF consume, so the
+    /// blocks pass through unchanged; only the header/total normalisation is applied.
+    /// </summary>
+    private FdsInvoiceData BuildFdsData(InvoiceDraftSession session)
+    {
+        var adm = (JObject)session.Admin.DeepClone();
+        var nw  = (JObject)session.New.DeepClone();
+        nw["total_net"]   = session.Sums.TotalNet;
+        nw["total_gross"] = session.Sums.TotalGross;
+        nw["title"]             = nw["invoicetitle"] ?? nw["title"] ?? "";
+        nw["provisionlocation"] = nw["loc"] ?? nw["provisionlocation"] ?? "";
+        nw["paymentterm"]       = adm["paymentterms"] ?? nw["paymentterm"] ?? "";
+        adm["customerid"]       = adm["customerid"] ?? adm["CustomerId"];
+
+        var vat = new JObject();
+        foreach (var kv in session.Sums.VatByRate) vat[kv.Key] = kv.Value;
+        var sms = new JObject
+        {
+            ["ttn"]    = session.Sums.TotalNet,
+            ["ttb"]    = session.Sums.TotalGross,
+            ["ttvat"]  = session.Sums.TotalVat,
+            ["tscn"]   = session.Sums.ServiceNet,
+            ["tscvat"] = session.Sums.ServiceVat,
+            ["vat"]    = vat
+        };
+
+        var jobj = new JObject
+        {
+            ["admin"] = adm,
+            ["new"]   = nw,
+            ["sms"]   = sms,
+            ["req"]   = session.Req.DeepClone()
+        };
+        return new FdsInvoiceData(jobj);
+    }
+
+    /// <summary>
+    /// Synthesises the <c>InvoiceRegistration</c> dictionary a draft PDF render needs,
+    /// straight from the cached session — so a preview requires no DB round-trip and no
+    /// client upload. Mirrors the columns <c>fds__getInvoice</c> would return for a draft.
+    /// </summary>
+    private GenericObjectDictionary SynthesizeRegistration(InvoiceDraftSession session)
+    {
+        string title = Str(session.New["invoicetitle"]).ne(Str(session.New["title"]));
+        string loc   = Str(session.New["provisionlocation"]).ne(Str(session.New["loc"]));
+        var d = new Dictionary<string, object>
+        {
+            ["Id"]                 = session.InvId,
+            ["InvoiceType"]        = Str(session.Admin["type"]).ne("R"),
+            ["InvoiceId"]          = "",
+            ["InvoiceTitle"]       = title,
+            ["SendToAddress"]      = Str(session.New["invoiceaddress"]),
+            ["SendToEmail"]        = Str(session.New["invoiceemail"]),
+            ["ProvisionLocation"]  = loc,
+            ["ProvisionPeriod"]    = Str(session.New["provisionperiod"]),
+            ["PaymentTerm"]        = Str(session.Admin["paymentterms"]).ne(Str(session.New["paymentterm"])),
+            ["InvoiceBalance"]     = session.Sums.TotalGross,
+            ["InvoiceBalance_net"] = session.Sums.TotalNet,
+            ["CustomValues"]       = Str(session.New["CustomValues"]),
+            ["InvoiceOptions"]     = BuildInvoiceOptions(session),
+            ["DateCreated"]        = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture)
+        };
+
+        int idx = 0;
+        foreach (var kv in session.Sums.VatByRate)
+        {
+            idx++;
+            if (idx > 2) break;
+            d[$"InvoiceVAT_{idx}"]    = kv.Key;
+            d[$"InvoiceVAT_net{idx}"] = kv.Value;
+        }
+        return new GenericObjectDictionary(d);
+    }
+
+    /// <summary>Builds the InvoiceOptions CSV (§13b + setmode) from the session admin flags — matches <see cref="FdsInvoiceData.BuildInvoiceOptions"/>.</summary>
+    private static string BuildInvoiceOptions(InvoiceDraftSession session)
+    {
+        var tokens = new List<string>();
+        if (AsBool(session.Admin["p13b"])) tokens.Add("§13b");
+        string setmode = Str(session.Admin["setmode"]).Trim().ToLowerInvariant();
+        if (setmode is "itemprices" or "setonly") tokens.Add("setmode:" + setmode);
+        return string.Join(",", tokens);
+    }
+
+    // ── token helpers ─────────────────────────────────────────────────────────
+    private static string Str(JToken? t) =>
+        t == null || t.Type == JTokenType.Null ? "" : t.Type == JTokenType.String ? t.Value<string>() ?? "" : t.ToString();
+
+    private static bool AsBool(JToken? t)
+    {
+        if (t == null || t.Type == JTokenType.Null) return false;
+        if (t.Type == JTokenType.Boolean) return t.Value<bool>();
+        string s = Str(t).Trim().ToLowerInvariant();
+        return s is "1" or "true" or "yes" or "ja" or "on";
+    }
+
+    private static JObject TryParseObject(string json)
+    {
+        if (!string.IsNullOrWhiteSpace(json) && json.TrimStart().StartsWith('{'))
+        {
+            try { return JObject.Parse(json); } catch { /* fall through */ }
+        }
+        return new JObject();
+    }
+
+    /// <summary>
+    /// Converts the editor's HTML (TinyMCE-wrapped inline edits, e.g. <c>&lt;p&gt;18.06.2026&lt;/p&gt;</c>)
+    /// to plain text: line-break-producing tags become newlines, remaining tags are stripped and
+    /// entities decoded. Multi-line fields (address, Leistungsort) keep their line breaks — the PDF
+    /// splits those on <c>\n</c>/<c>&lt;br&gt;</c> — while single-line fields collapse to one line.
+    /// Blank lines are removed so a stray <c>&lt;p&gt;&lt;/p&gt;</c> never becomes an empty row.
+    /// </summary>
+    internal static string HtmlToPlain(string? raw)
+    {
+        if (string.IsNullOrEmpty(raw)) return "";
+        if (raw.IndexOf('<') < 0 && raw.IndexOf('&') < 0) return raw.Trim();
+
+        // Turn line-break / block-close tags into newlines before stripping the rest.
+        string s = Regex.Replace(raw, @"<\s*br\s*/?\s*>", "\n", RegexOptions.IgnoreCase);
+        s = Regex.Replace(s, @"</\s*(p|div|li|tr|h[1-6])\s*>", "\n", RegexOptions.IgnoreCase);
+
+        var doc = new HtmlAgilityPack.HtmlDocument();
+        doc.LoadHtml(s);
+        string text = System.Net.WebUtility.HtmlDecode(doc.DocumentNode.InnerText);
+
+        var lines = text.Replace("\r\n", "\n").Replace('\r', '\n')
+                        .Split('\n')
+                        .Select(l => l.Trim())
+                        .Where(l => l.Length > 0);
+        return string.Join("\n", lines).Trim();
+    }
+}

Fuchs/Services/InvoiceDraftExpiryService.cs

@@ -0,0 +1,68 @@
+using Fuchs.Notifications;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Background monitor for the invoice draft cache (ADR 0006). Because a draft's
+/// truth lives only in server memory until the user saves, idle sessions must not
+/// vanish silently: this service warns the editing browser <b>before</b> a session's
+/// idle TTL lapses ("bitte zwischenspeichern"), and when the TTL is finally reached
+/// it evicts the session and tells the browser to close the editor with a reason.
+/// All hints travel over the <see cref="DraftPreviewHub"/> via <see cref="IDraftNotifier"/>.
+/// </summary>
+public sealed class InvoiceDraftExpiryService : BackgroundService
+{
+    private readonly IInvoiceDraftCache _cache;
+    private readonly IDraftNotifier _notifier;
+    private readonly ILogger<InvoiceDraftExpiryService> _logger;
+    private readonly TimeSpan _warnLead;
+    private readonly TimeSpan _interval;
+
+    public InvoiceDraftExpiryService(IInvoiceDraftCache cache, IDraftNotifier notifier,
+        IConfiguration configuration, ILogger<InvoiceDraftExpiryService> logger)
+    {
+        _cache = cache;
+        _notifier = notifier;
+        _logger = logger;
+        int warnMinutes = configuration.GetValue("Fuchs:DraftEditing:ExpiryWarnMinutes", 5);
+        _warnLead = TimeSpan.FromMinutes(Math.Clamp(warnMinutes, 1, Math.Max(1, (int)cache.IdleTtl.TotalMinutes - 1)));
+        _interval = TimeSpan.FromSeconds(30);
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        using var timer = new PeriodicTimer(_interval);
+        try
+        {
+            while (await timer.WaitForNextTickAsync(stoppingToken))
+                await SweepAsync(stoppingToken);
+        }
+        catch (OperationCanceledException) { /* shutting down */ }
+    }
+
+    /// <summary>One pass over all live sessions. Internal so it can be driven directly from unit tests.</summary>
+    internal async Task SweepAsync(CancellationToken cancellationToken)
+    {
+        DateTime now = DateTime.UtcNow;
+        foreach (var session in _cache.Snapshot())
+        {
+            TimeSpan idle = now - session.LastAccessUtc;
+            if (idle >= _cache.IdleTtl)
+            {
+                _cache.Remove(session.Token);
+                _logger.LogInformation("Draft {Token} evicted after {Idle} idle (user={User})",
+                    session.Token, idle, session.UserAccountId);
+                await _notifier.SignalClosedAsync(session.Token, "expired", cancellationToken);
+            }
+            else if (idle >= _cache.IdleTtl - _warnLead && !session.ExpiryWarningSent)
+            {
+                session.ExpiryWarningSent = true;
+                int secondsLeft = (int)Math.Max(0, (_cache.IdleTtl - idle).TotalSeconds);
+                await _notifier.SignalExpiringAsync(session.Token, secondsLeft, cancellationToken);
+            }
+        }
+    }
+}

Fuchs/Services/InvoiceService.cs

@@ -63,10 +63,64 @@ public class InvoiceService : IInvoiceService
 
         inv.InvoiceRegistration = new GenericObjectDictionary(dset.Table("inv").FirstRow.toObjectDictionary());
         inv.IsDraft = inv.InvoiceRegistration.getItem("IsFinal", false) is not true;
-        _logger.LogDebug("LoadInvoiceAsync loaded id={Id} draft={Draft}", inv.Id, inv.IsDraft);
+        // Reconstruct the service-request blocks + line items so the PDF renders the positions.
+        // Without this the reloaded/finalized invoice showed an empty item table (only the header
+        // + totals came from InvoiceRegistration), i.e. it did not match the cached preview.
+        inv.Req = BuildPdfRequestBlocks(dset);
+        _logger.LogDebug("LoadInvoiceAsync loaded id={Id} draft={Draft} blocks={Blocks}", inv.Id, inv.IsDraft, inv.Req?.Count ?? 0);
         return inv;
     }
 
+    /// <summary>
+    /// Rebuilds the invoice's service-request groups and line items from the persisted
+    /// <c>req</c>/<c>itm</c> tables (<c>fds__getInvoice</c>) into the exact block shape the PDF
+    /// consumes (<see cref="FdsInvoiceData.InvoiceBlocks"/> → item contract
+    /// <c>type/title/desc/qty/price_net/total_net</c>). Item order follows the persisted
+    /// <c>SortOrder</c>, so a reordered draft renders in its saved order — making the finalized
+    /// PDF and the re-downloaded (<c>idoc</c>) document identical to the cached preview.
+    /// </summary>
+    private static List<Dictionary<string, object>> BuildPdfRequestBlocks(SQLDataSet dset)
+    {
+        var blocks = new List<Dictionary<string, object>>();
+        if (!dset.Contains("req")) return blocks;
+
+        var reqTable = dset.Tables("req");
+        string reqSort = reqTable.Columns.Contains("order") ? "order" : "";
+        foreach (DataRow rq in reqTable.Select("", reqSort))
+        {
+            var rdic = rq.toObjectDictionary();
+            var items = new List<Dictionary<string, object?>>();
+            if (dset.Contains("itm"))
+            {
+                var itmTable = dset.Tables("itm");
+                string itmSort = itmTable.Columns.Contains("order") ? "order" : "";
+                foreach (DataRow it in itmTable.Select($"[InvRqId] = '{rdic.nz("Id")}'", itmSort))
+                {
+                    var d = it.toObjectDictionary();
+                    // The persisted "Text" holds the item's rendered HTML (the editor's co.t); it is
+                    // the full title+description, so it maps to the contract's desc (title stays empty).
+                    items.Add(new Dictionary<string, object?>
+                    {
+                        ["id"]        = d.nz("mfr__item"),
+                        ["type"]      = d.nz("Type"),
+                        ["title"]     = "",
+                        ["desc"]      = d.nz("Text"),
+                        ["qty"]       = d.nz("Quantity"),
+                        ["price_net"] = d.no("value", 0),
+                        ["total_net"] = d.no("value_total", 0)
+                    });
+                }
+            }
+            blocks.Add(new Dictionary<string, object>
+            {
+                ["Id"]    = rdic.nz("mfr__servicerequest"),
+                ["text"]  = System.Net.WebUtility.HtmlDecode(rdic.nz("title")),
+                ["items"] = items
+            });
+        }
+        return blocks;
+    }
+
     public async Task<FdsInvoiceData> RegisterInvoiceAsync(FdsInvoiceData invoice, bool change, string invId,
         string userAccountId, DatabaseSecurity dbSec)
     {
@@ -212,7 +266,7 @@ public class InvoiceService : IInvoiceService
         var reg = invoice.InvoiceRegistration;
         var tb = new FuchsPdf.FdsTextBlocks
         {
-            AdminRef       = reg?.getString("Id") ?? "",
+            AdminRef       = (reg?.getString("InvoiceId") ?? "").ne(reg?.getString("Id") ?? ""),
             Address        = reg?.getString("SendToAddress") is { Length: > 0 } sa
                 ? sa.Replace("<br>", "\n").Replace("<br/>", "\n").Split('\n').Select(t => t.Trim()).ToArray()
                 : Array.Empty<string>(),

Fuchs/Services/ReminderDraftCache.cs

@@ -0,0 +1,61 @@
+using System.Collections.Concurrent;
+using Fuchs.intranet;
+using Microsoft.Extensions.Configuration;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Single-instance, in-memory implementation of <see cref="IReminderDraftCache"/> backed
+/// by a <see cref="ConcurrentDictionary{TKey,TValue}"/> keyed by session token — the
+/// reminder mirror of <see cref="InvoiceDraftCache"/>. A plain dictionary (rather than
+/// <c>IMemoryCache</c>) is used on purpose: the <see cref="ReminderDraftExpiryService"/>
+/// needs to enumerate sessions and warn the user <b>before</b> eviction, which opaque
+/// cache-entry expiry does not allow.
+///
+/// Idle TTL and the pre-expiry warning lead time are shared with invoices under
+/// <c>Fuchs:DraftEditing</c> (<c>IdleMinutes</c> / <c>ExpiryWarnMinutes</c>).
+/// </summary>
+public sealed class ReminderDraftCache : IReminderDraftCache
+{
+    private readonly ConcurrentDictionary<string, ReminderDraftSession> _sessions = new(StringComparer.Ordinal);
+
+    public TimeSpan IdleTtl { get; }
+    /// <summary>How long before the idle TTL a warning is emitted to the user.</summary>
+    public TimeSpan ExpiryWarnLead { get; }
+
+    public ReminderDraftCache(IConfiguration configuration)
+    {
+        int idleMinutes = configuration.GetValue("Fuchs:DraftEditing:IdleMinutes", 30);
+        int warnMinutes = configuration.GetValue("Fuchs:DraftEditing:ExpiryWarnMinutes", 5);
+        IdleTtl        = TimeSpan.FromMinutes(Math.Max(1, idleMinutes));
+        ExpiryWarnLead = TimeSpan.FromMinutes(Math.Clamp(warnMinutes, 1, Math.Max(1, idleMinutes - 1)));
+    }
+
+    public void Set(ReminderDraftSession session)
+    {
+        if (string.IsNullOrEmpty(session.Token)) throw new ArgumentException("Session has no token.", nameof(session));
+        session.Touch();
+        _sessions[session.Token] = session;
+    }
+
+    public ReminderDraftSession? Get(string token)
+    {
+        if (string.IsNullOrEmpty(token)) return null;
+        if (_sessions.TryGetValue(token, out var s))
+        {
+            s.Touch();
+            // A touch resets the idle window, so a fresh warning is due next time it lapses.
+            s.ExpiryWarningSent = false;
+            return s;
+        }
+        return null;
+    }
+
+    public ReminderDraftSession? Remove(string token)
+    {
+        if (string.IsNullOrEmpty(token)) return null;
+        return _sessions.TryRemove(token, out var s) ? s : null;
+    }
+
+    public IReadOnlyList<ReminderDraftSession> Snapshot() => _sessions.Values.ToList();
+}

Fuchs/Services/ReminderDraftEditService.cs

@@ -0,0 +1,275 @@
+using System.Globalization;
+using Fuchs.intranet;
+using Microsoft.Extensions.Logging;
+using MigraDoc.DocumentObjectModel;
+using Newtonsoft.Json.Linq;
+using OCORE.security;
+using static OCORE.commons;
+using static OCORE.OCORE_dictionaries;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Backend-authoritative reminder draft editing (ADR 0006) — the reminder mirror of
+/// <see cref="InvoiceDraftEditService"/>. Holds the truth in a
+/// <see cref="ReminderDraftSession"/> (via <see cref="IReminderDraftCache"/>), applies
+/// single edits, aggregates the open amount with <see cref="ReminderDraftCalculator"/>,
+/// renders previews and flushes to the DB by reusing the existing
+/// <see cref="IReminderService"/> registration path — no new persistence. The session
+/// stores the editor's own block shape (<c>new</c>/<c>rem</c>), which the PDF/persistence
+/// already consume, so nothing is re-shaped server-side.
+/// </summary>
+public sealed class ReminderDraftEditService : IReminderDraftService
+{
+    private readonly IReminderDraftCache _cache;
+    private readonly IReminderService _reminders;
+    private readonly ILogger<ReminderDraftEditService> _logger;
+
+    public ReminderDraftEditService(IReminderDraftCache cache, IReminderService reminders,
+        ILogger<ReminderDraftEditService> logger)
+    {
+        _cache = cache;
+        _reminders = reminders;
+        _logger = logger;
+    }
+
+    // ── Open ─────────────────────────────────────────────────────────────────
+    public ReminderDraftSession OpenFromPayload(JObject payload, string userAccountId)
+    {
+        var session = new ReminderDraftSession
+        {
+            Token = NewToken(),
+            UserAccountId = userAccountId,
+            RemId = payload["remid"]?.Value<string>() ?? payload["id"]?.Value<string>() ?? ""
+        };
+        session.New = payload["new"] as JObject ?? new JObject();
+        session.Rem = payload["rem"] as JObject ?? new JObject();
+        Refresh(session);
+        _cache.Set(session);
+        _logger.LogInformation("Reminder draft session {Token} opened from payload (remId={RemId}, user={User})",
+            session.Token, session.RemId, userAccountId);
+        return session;
+    }
+
+    public ReminderDraftSession? Get(string token) => _cache.Get(token);
+
+    // ── Patch ──────────────────────────────────────────────────────────────────
+    public ReminderDraftSession? ApplyPatch(string token, ReminderDraftDelta delta)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+
+        string oldValue = "", newValue = "";
+        bool mutated = ApplyDelta(session, delta, ref oldValue, ref newValue);
+        if (!mutated)
+        {
+            _logger.LogDebug("Reminder draft {Token}: no-op patch target={Target} ref={Ref}", token, delta.Target, delta.Ref);
+            return session;
+        }
+
+        Refresh(session);
+        session.Version++;
+        session.History.Add(new ChangeHistoryEntry
+        {
+            UserAccountId = session.UserAccountId,
+            Target = delta.Target,
+            Ref = delta.Ref,
+            OldValue = oldValue,
+            NewValue = newValue,
+            Version = session.Version
+        });
+        _cache.Set(session);
+        return session;
+    }
+
+    /// <summary>
+    /// Applies one delta to the payload; returns whether anything changed and captures the prior
+    /// and new value for the change history. Scalar text fields are sanitised from the editor's
+    /// HTML (TinyMCE wraps inline edits in <c>&lt;p&gt;…&lt;/p&gt;</c>) to plain text (via
+    /// <see cref="InvoiceDraftEditService.HtmlToPlain"/>) — the backend is the single source of
+    /// truth (ADR 0006), so no HTML ever reaches the DB or the PDF.
+    /// </summary>
+    private static bool ApplyDelta(ReminderDraftSession s, ReminderDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        switch (d.Target)
+        {
+            case "email":        return SetNewText(s, "invoiceemail", d, ref oldValue, ref newValue);
+            case "address":      return SetNewText(s, "invoiceaddress", d, ref oldValue, ref newValue);
+            case "subject":      return SetNewText(s, "subject", d, ref oldValue, ref newValue);
+            case "text":         return SetNewText(s, "text", d, ref oldValue, ref newValue);
+            case "amount":       return SetNewNumber(s, "amount", d, ref oldValue, ref newValue);
+            case "amount_payed": return SetNewNumber(s, "amount_payed", d, ref oldValue, ref newValue);
+            case "contact":      return SetContact(s, d, ref oldValue, ref newValue);
+            default:             return false;
+        }
+    }
+
+    private static bool SetNewText(ReminderDraftSession s, string key, ReminderDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        oldValue = Str(s.New[key]);
+        newValue = InvoiceDraftEditService.HtmlToPlain(d.ValueString);
+        s.New[key] = newValue;
+        return true;
+    }
+
+    /// <summary>Stores a numeric field, normalising German/invariant input to an invariant decimal string.</summary>
+    private static bool SetNewNumber(ReminderDraftSession s, string key, ReminderDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        oldValue = Str(s.New[key]);
+        decimal parsed = ReminderDraftCalculator.Dec(d.Value ?? JValue.CreateString(InvoiceDraftEditService.HtmlToPlain(d.ValueString)));
+        newValue = parsed.ToString(CultureInfo.InvariantCulture);
+        s.New[key] = newValue;
+        return true;
+    }
+
+    private static bool SetContact(ReminderDraftSession s, ReminderDraftDelta d, ref string oldValue, ref string newValue)
+    {
+        JObject prev = TryParseObject(Str(s.New["CustomValues"]));
+        oldValue = ContactLabel(Str(prev["contactName"]), Str(prev["contactEmail"]));
+        JObject cvo = (JObject)prev.DeepClone();
+        if (d.Value is JObject vo)
+        {
+            cvo["contactName"]  = vo["name"] ?? vo["contactName"] ?? "";
+            cvo["contactEmail"] = vo["email"] ?? vo["contactEmail"] ?? "";
+        }
+        s.New["CustomValues"] = cvo.ToString(Newtonsoft.Json.Formatting.None);
+        newValue = ContactLabel(Str(cvo["contactName"]), Str(cvo["contactEmail"]));
+        return true;
+    }
+
+    private static string ContactLabel(string name, string email) =>
+        string.IsNullOrEmpty(name) ? email : string.IsNullOrEmpty(email) ? name : $"{name} <{email}>";
+
+    // ── View state / history ────────────────────────────────────────────────
+    public object BuildState(ReminderDraftSession session)
+    {
+        session.Touch();
+        return new
+        {
+            token   = session.Token,
+            version = session.Version,
+            remid   = session.RemId,
+            isDraft = session.IsDraft,
+            @new    = session.New,
+            rem     = session.Rem,
+            sums    = new
+            {
+                amount_total = session.Sums.AmountTotal,
+                amount_payed = session.Sums.AmountPayed,
+                amount_open  = session.Sums.AmountOpen
+            },
+            validation = session.ValidationMessages.Select(v => new { field = v.Field, severity = v.Severity, message = v.Message }),
+            historyCount = session.History.Count
+        };
+    }
+
+    public IReadOnlyList<ChangeHistoryEntry> GetHistory(string token) =>
+        _cache.Get(token)?.History ?? (IReadOnlyList<ChangeHistoryEntry>)Array.Empty<ChangeHistoryEntry>();
+
+    // ── Flush / preview ────────────────────────────────────────────────────────
+    public async Task<FdsReminderData?> FlushToDbAsync(string token, string userAccountId, DatabaseSecurity dbSec)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+
+        var fds = BuildReminderData(session);
+        bool change = !string.IsNullOrEmpty(session.RemId);
+        var reg = await _reminders.RegisterReminderAsync(fds, change, session.RemId, userAccountId, dbSec);
+        if (!string.IsNullOrEmpty(reg.Id))
+        {
+            session.RemId = reg.Id;
+            _cache.Set(session);
+            _logger.LogInformation("Reminder draft {Token} flushed to DB reminder {RemId} (change={Change}, user={User})",
+                token, reg.Id, change, userAccountId);
+        }
+        return reg;
+    }
+
+    public Document? RenderPreview(string token)
+    {
+        var session = _cache.Get(token);
+        if (session == null) return null;
+        var fds = BuildReminderData(session);
+        fds.ReminderRegistration = SynthesizeRegistration(session);
+        fds.IsDraft = true;
+        return _reminders.GenerateReminderPdf(fds, draft: true);
+    }
+
+    public bool Close(string token) => _cache.Remove(token) != null;
+
+    // ── Internals ──────────────────────────────────────────────────────────────
+    private static void Refresh(ReminderDraftSession session)
+    {
+        ReminderDraftCalculator.RecomputeTotals(session);
+        ReminderDraftCalculator.Validate(session);
+    }
+
+    private static string NewToken() => Guid.NewGuid().ToString("N");
+
+    /// <summary>
+    /// Builds the <see cref="FdsReminderData"/> from the session — the server-side equivalent of
+    /// the editor's <c>remc</c> payload. The session already holds the editor's <c>new</c>/<c>rem</c>
+    /// shape that registration consumes, so the blocks pass through unchanged.
+    /// </summary>
+    private static FdsReminderData BuildReminderData(ReminderDraftSession session)
+    {
+        var jobj = new JObject
+        {
+            ["new"] = session.New.DeepClone(),
+            ["rem"] = session.Rem.DeepClone()
+        };
+        return new FdsReminderData(jobj);
+    }
+
+    /// <summary>
+    /// Synthesises the <c>ReminderRegistration</c> dictionary a draft PDF render needs, straight
+    /// from the cached session — so a preview requires no DB round-trip and no client upload.
+    /// Mirrors the columns <c>fds__getReminder</c>/<c>fds__createReminder</c> would return for a
+    /// draft, including the single-invoice <c>invoices</c> row the reminder table renders.
+    /// </summary>
+    private static GenericObjectDictionary SynthesizeRegistration(ReminderDraftSession session)
+    {
+        string invoiceId = Str(session.Rem["invoiceid"]).ne(Str(session.Rem["InvoiceId"]));
+        var invoices = new JArray
+        {
+            new JObject
+            {
+                ["InvoiceDate"]    = Str(session.Rem["invoicedate"]),
+                ["DocumentName"]   = "",
+                ["InvoiceTitle"]   = string.IsNullOrEmpty(invoiceId) ? "" : $"Rechnung {invoiceId}",
+                ["InvoiceBalance"] = session.Sums.AmountTotal,
+                ["amount_open"]    = session.Sums.AmountOpen
+            }
+        };
+
+        var d = new Dictionary<string, object>
+        {
+            ["Id"]            = session.RemId,
+            ["type"]          = Str(session.Rem["type"]).ne("R"),
+            ["subject"]       = Str(session.New["subject"]),
+            ["SendToAddress"] = Str(session.New["invoiceaddress"]),
+            ["SendToEmail"]   = Str(session.New["invoiceemail"]),
+            ["InvoiceId"]     = invoiceId,
+            ["amount_open"]   = session.Sums.AmountOpen,
+            ["PaymentTerm"]   = Str(session.Rem["paymentterm"]),
+            ["invoices"]      = invoices,
+            ["CustomValues"]  = Str(session.New["CustomValues"]),
+            ["IsFinal"]       = false,
+            ["DateCreated"]   = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture)
+        };
+        return new GenericObjectDictionary(d);
+    }
+
+    // ── token helpers ─────────────────────────────────────────────────────────
+    private static string Str(JToken? t) =>
+        t == null || t.Type == JTokenType.Null ? "" : t.Type == JTokenType.String ? t.Value<string>() ?? "" : t.ToString();
+
+    private static JObject TryParseObject(string json)
+    {
+        if (!string.IsNullOrWhiteSpace(json) && json.TrimStart().StartsWith('{'))
+        {
+            try { return JObject.Parse(json); } catch { /* fall through */ }
+        }
+        return new JObject();
+    }
+}

Fuchs/Services/ReminderDraftExpiryService.cs

@@ -0,0 +1,69 @@
+using Fuchs.Notifications;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Fuchs.Services;
+
+/// <summary>
+/// Background monitor for the reminder draft cache (ADR 0006) — the reminder mirror of
+/// <see cref="InvoiceDraftExpiryService"/>. Because a draft's truth lives only in server
+/// memory until the user saves, idle sessions must not vanish silently: this service warns
+/// the editing browser <b>before</b> a session's idle TTL lapses ("bitte zwischenspeichern"),
+/// and when the TTL is finally reached it evicts the session and tells the browser to close
+/// the editor with a reason. All hints travel over the shared <see cref="DraftPreviewHub"/>
+/// via <see cref="IDraftNotifier"/> (the token-keyed groups serve invoices and reminders alike).
+/// </summary>
+public sealed class ReminderDraftExpiryService : BackgroundService
+{
+    private readonly IReminderDraftCache _cache;
+    private readonly IDraftNotifier _notifier;
+    private readonly ILogger<ReminderDraftExpiryService> _logger;
+    private readonly TimeSpan _warnLead;
+    private readonly TimeSpan _interval;
+
+    public ReminderDraftExpiryService(IReminderDraftCache cache, IDraftNotifier notifier,
+        IConfiguration configuration, ILogger<ReminderDraftExpiryService> logger)
+    {
+        _cache = cache;
+        _notifier = notifier;
+        _logger = logger;
+        int warnMinutes = configuration.GetValue("Fuchs:DraftEditing:ExpiryWarnMinutes", 5);
+        _warnLead = TimeSpan.FromMinutes(Math.Clamp(warnMinutes, 1, Math.Max(1, (int)cache.IdleTtl.TotalMinutes - 1)));
+        _interval = TimeSpan.FromSeconds(30);
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        using var timer = new PeriodicTimer(_interval);
+        try
+        {
+            while (await timer.WaitForNextTickAsync(stoppingToken))
+                await SweepAsync(stoppingToken);
+        }
+        catch (OperationCanceledException) { /* shutting down */ }
+    }
+
+    /// <summary>One pass over all live sessions. Internal so it can be driven directly from unit tests.</summary>
+    internal async Task SweepAsync(CancellationToken cancellationToken)
+    {
+        DateTime now = DateTime.UtcNow;
+        foreach (var session in _cache.Snapshot())
+        {
+            TimeSpan idle = now - session.LastAccessUtc;
+            if (idle >= _cache.IdleTtl)
+            {
+                _cache.Remove(session.Token);
+                _logger.LogInformation("Reminder draft {Token} evicted after {Idle} idle (user={User})",
+                    session.Token, idle, session.UserAccountId);
+                await _notifier.SignalClosedAsync(session.Token, "expired", cancellationToken);
+            }
+            else if (idle >= _cache.IdleTtl - _warnLead && !session.ExpiryWarningSent)
+            {
+                session.ExpiryWarningSent = true;
+                int secondsLeft = (int)Math.Max(0, (_cache.IdleTtl - idle).TotalSeconds);
+                await _notifier.SignalExpiringAsync(session.Token, secondsLeft, cancellationToken);
+            }
+        }
+    }
+}

Fuchs/appsettings.Development.json

@@ -26,6 +26,9 @@
       "CheckMfr": false,
       "CheckPdfLicense": true
     },
+    "Mailer": {
+      "Enabled": true
+    },
     "Email": {
       "OverrideRecipient": "service@emails.processweb.de"
     },

Fuchs/code/FdsInvoiceData.cs

@@ -19,7 +19,7 @@ public class FdsInvoiceData
     public GenericObjectDictionary? Admin      { get; private set; }
     public GenericObjectDictionary? NewValues  { get; private set; }
     public GenericObjectDictionary? Sms        { get; private set; }
-    public List<Dictionary<string, object>>? Req { get; private set; }
+    public List<Dictionary<string, object>>? Req { get; internal set; }
 
     public GenericObjectDictionary? InvoiceRegistration { get; internal set; }
     public bool IsDraft { get; internal set; } = true;
@@ -46,9 +46,25 @@ public class FdsInvoiceData
         get
         {
             var result = new List<Dictionary<string, object?>>();
+            foreach (var block in InvoiceBlocks) result.AddRange(block.Items);
+            return result;
+        }
+    }
+
+    /// <summary>
+    /// The service-request groups as they should render on the invoice: each block carries its
+    /// heading (the section title the editor shows) and its line items. The PDF renders a heading
+    /// row per block followed by that block's items, so the online editor and the PDF stay in sync.
+    /// </summary>
+    public List<InvoiceBlock> InvoiceBlocks
+    {
+        get
+        {
+            var result = new List<InvoiceBlock>();
             if (Req == null) return result;
             foreach (var req in Req)
             {
+                var items = new List<Dictionary<string, object?>>();
                 if (req.TryGetValue("items", out var itmsObj))
                 {
                     IEnumerable<Dictionary<string, object?>>? itms =
@@ -56,8 +72,12 @@ public class FdsInvoiceData
                         ?? (itmsObj is JArray ja
                             ? ja.ToObject<List<Dictionary<string, object?>>>()
                             : null);
-                    if (itms != null) result.AddRange(itms);
+                    if (itms != null) items.AddRange(itms);
                 }
+                string heading = "";
+                if (req.TryGetValue("text", out var th) && th != null) heading = th.ToString() ?? "";
+                if (heading.Length == 0 && req.TryGetValue("nme", out var nh) && nh != null) heading = nh.ToString() ?? "";
+                result.Add(new InvoiceBlock { Heading = heading, Items = items });
             }
             return result;
         }
@@ -196,3 +216,12 @@ public class FdsInvoiceData
         return double.TryParse(s, NumberStyles.Any, CultureInfo.InvariantCulture, out var d) ? d : 0;
     }
 }
+
+/// <summary>A service-request group as it renders on the invoice: a heading plus its line items.</summary>
+public sealed class InvoiceBlock
+{
+    /// <summary>The section heading (editor's <c>text</c>/<c>nme</c>); empty when the group has none.</summary>
+    public string Heading { get; init; } = "";
+    /// <summary>The group's line items (the editor's <c>items</c> contract).</summary>
+    public List<Dictionary<string, object?>> Items { get; init; } = new();
+}

Fuchs/code/FuchsPdf.cs

@@ -137,6 +137,30 @@ public static class FuchsPdf
     public static string TranslatePaymentTerm(string pt) =>
         pt.Replace("wd", " Werktagen").Replace("d", " Tagen").Replace("wk", " Wochen").ne("10 Tagen");
 
+    /// <summary>
+    /// Maps one editor item-contract entry to a display line, mirroring the online editor: the
+    /// item's own price/total is shown, a set header is emphasised, and free-text/heading lines
+    /// (type <c>text</c>/<c>title</c>) show neither a price nor a position number. This is the flat
+    /// (non-collapsing) rendering used for every set mode except the explicit <c>setonly</c>.
+    /// </summary>
+    private static InvoiceSetLine MapItemToLine(Dictionary<string, object?> i)
+    {
+        string type = i.nz("type", "").ToLowerInvariant();
+        bool isText  = type is "text" or "title";
+        ParseDec(i.no("price_net", 0), out decimal price);
+        ParseDec(i.no("total_net", 0), out decimal total);
+        return new InvoiceSetLine
+        {
+            Title       = i.nz("title", ""),
+            Desc        = i.nz("desc", ""),
+            Qty         = i.nz("qty", ""),
+            PriceNet    = price,
+            TotalNet    = total,
+            ShowPrice   = !isText,
+            IsSetHeader = type == "set"
+        };
+    }
+
     /// <summary>
     /// Parses a numeric value coming from JSON deserialization (long/double), SQL
     /// (decimal), or an already-invariant numeric string. Numeric CLR types are
@@ -593,30 +617,49 @@ public static class FuchsPdf
             hRow.Cells[i].Format.Alignment = i >= 2 ? ParagraphAlignment.Right : ParagraphAlignment.Left;
         }
 
-        // Data rows — resolved through the set-display mode (see InvoiceSetPricing).
+        // Data rows — grouped by service-request block (see FdsInvoiceData.InvoiceBlocks).
-        // For invoices without sets this passes items through unchanged; for sets it
+        // Per the product decision the PDF must mirror the online editor exactly: each section
-        // emits set header + members per the chosen mode, blanking price cells where
+        // prints its heading, every position shows its own price, and positions are numbered the
-        // a line should show no price. Totals come from the registration balance, so
+        // same way the editor numbers them (every line except free-text/heading lines, including a
-        // the mode is purely presentational.
+        // set header). Set-display collapsing is honoured only for the explicit SetOnly mode; every
+        // other mode renders the items flat, so nothing is silently blanked or renumbered.
         var setMode = InvoiceSetPricing.ModeFromInvoiceOptions(inv.InvoiceRegistration?.getString("InvoiceOptions"));
-        int pos = 1;
+        int pos = 0;
-        foreach (var line in InvoiceSetPricing.Build(inv.InvoiceItems, setMode))
+        foreach (var block in inv.InvoiceBlocks)
         {
-            var row = tbl.AddRow();
+            if (!string.IsNullOrWhiteSpace(block.Heading))
-            row.HeightRule = RowHeightRule.Auto;
+            {
-            row.Cells[0].AddParagraph(pos.ToString()).Style = "TblCell_Base";
+                var hr = tbl.AddRow();
-            var titleCell = row.Cells[1].AddParagraph();
+                hr.HeightRule = RowHeightRule.Auto;
-            titleCell.Style = "TblCell_RTitle";
+                hr.Cells[1].MergeRight = 3;                 // span Bezeichnung … Gesamtpreis
-            if (line.IsSetHeader) titleCell.AddFormattedText(line.Title, TextFormat.Bold);
+                hr.Cells[1].AddParagraph().WithStyle("TblCell_RTitle").AddFormattedText(block.Heading, TextFormat.Bold);
-            else                  titleCell.AddText(line.Title);
+            }
-            if (!string.IsNullOrEmpty(line.Desc)) row.Cells[1].AddHtml($"<div>{line.Desc}</div>");
+
-            row.Cells[2].AddParagraph(line.Qty).Style = "TblCell_Base";
+            var lines = setMode == SetDisplayMode.SetOnly && InvoiceSetPricing.ContainsSets(block.Items)
-            row.Cells[3].AddParagraph(line.ShowPrice ? Currency(line.PriceNet) : "").Style = "TblCell_Base";
+                ? InvoiceSetPricing.Build(block.Items, SetDisplayMode.SetOnly)   // only this mode collapses members
-            row.Cells[4].AddParagraph(line.ShowPrice ? Currency(line.TotalNet) : "").Style = "TblCell_RSum";
+                : block.Items.Select(MapItemToLine).ToList();                   // flat: faithful mirror of the editor
-            row.Cells[2].Format.Alignment = ParagraphAlignment.Right;
+
-            row.Cells[3].Format.Alignment = ParagraphAlignment.Right;
+            foreach (var line in lines)
-            row.Cells[4].Format.Alignment = ParagraphAlignment.Right;
+            {
-            pos++;
+                bool numbered = line.IsSetHeader || line.ShowPrice;             // free-text/heading lines carry no number
+                var row = tbl.AddRow();
+                row.HeightRule = RowHeightRule.Auto;
+                row.Cells[0].AddParagraph(numbered ? (++pos).ToString() : "").Style = "TblCell_Base";
+                if (!string.IsNullOrEmpty(line.Title))     // skip the empty paragraph that added a blank line before free text
+                {
+                    var titleCell = row.Cells[1].AddParagraph();
+                    titleCell.Style = "TblCell_RTitle";
+                    if (line.IsSetHeader) titleCell.AddFormattedText(line.Title, TextFormat.Bold);
+                    else                  titleCell.AddText(line.Title);
+                }
+                if (!string.IsNullOrEmpty(line.Desc)) row.Cells[1].AddHtml($"<div>{line.Desc}</div>");
+                row.Cells[2].AddParagraph(line.Qty).Style = "TblCell_Base";
+                row.Cells[3].AddParagraph(line.ShowPrice ? Currency(line.PriceNet) : "").Style = "TblCell_Base";
+                row.Cells[4].AddParagraph(line.ShowPrice ? Currency(line.TotalNet) : "").Style = "TblCell_RSum";
+                row.Cells[2].Format.Alignment = ParagraphAlignment.Right;
+                row.Cells[3].Format.Alignment = ParagraphAlignment.Right;
+                row.Cells[4].Format.Alignment = ParagraphAlignment.Right;
+            }
         }
 
         // Totals

Fuchs/code/InvoiceDraftCalculator.cs

@@ -0,0 +1,177 @@
+using System.Globalization;
+using Newtonsoft.Json.Linq;
+
+namespace Fuchs.intranet;
+
+/// <summary>
+/// Server-side, pure aggregation of an invoice draft's totals/VAT — the authoritative
+/// replacement for the browser's <c>invSumUpdate</c> footer math (ADR 0006). The user's
+/// requirement is that the <b>sums</b> live in the backend cache, not the frontend.
+///
+/// It reads each block's persisted line contract (<c>block.itm</c> = the editor's <c>co</c>
+/// objects: <c>vt</c>=net, <c>vv</c>=VAT, <c>vs</c>=service-net, <c>vsv</c>=service-VAT,
+/// <c>vat</c>=rate) — exactly the shape the editor already posts and the PDF/persistence
+/// already consume — so no line data is re-derived or re-shaped. It then applies the §13b
+/// reverse-charge rule and validates. Static/pure, hence exhaustively unit-testable.
+/// </summary>
+public static class InvoiceDraftCalculator
+{
+    /// <summary>
+    /// Aggregates every block's line values into the draft's totals — the port of
+    /// <c>invSumUpdate</c>'s <c>csms</c> accumulation plus §13b (VAT suppressed → gross = net).
+    /// VAT is grouped by the line's rate string (matching the editor's <c>sms.vat</c> map).
+    /// </summary>
+    public static void RecomputeTotals(InvoiceDraftSession session)
+    {
+        var sums = new InvoiceDraftSums();
+        bool p13b = Flag(session.Admin, "p13b");
+
+        foreach (var blockTok in session.Req)
+        {
+            if (blockTok is not JObject block) continue;
+            decimal blockNet = 0;
+            string blockId = Str(block["Id"]);
+            if (block["itm"] is JArray lines)
+            {
+                foreach (var lineTok in lines)
+                {
+                    if (lineTok is not JObject co) continue;
+                    decimal netVal = Dec(co["vt"]);
+                    decimal vatVal = Dec(co["vv"]);
+                    decimal svcNet = Dec(co["vs"]);
+                    decimal svcVat = Dec(co["vsv"]);
+
+                    sums.ServiceNet += svcNet;
+                    sums.ServiceVat += svcVat;
+                    sums.TotalNet   += netVal;
+                    sums.TotalVat   += vatVal;
+                    sums.TotalGross += netVal + vatVal;
+                    blockNet        += netVal;
+
+                    string rate = NormalizeRate(Str(co["vat"]));
+                    if (rate.Length > 0)
+                        sums.VatByRate[rate] = sums.VatByRate.GetValueOrDefault(rate) + vatVal;
+                }
+            }
+            if (!string.IsNullOrEmpty(blockId))
+                sums.NetByBlock[blockId] = sums.NetByBlock.GetValueOrDefault(blockId) + blockNet;
+        }
+
+        if (p13b)
+        {
+            // Reverse-charge: no VAT lines, gross equals net (mirrors invSumUpdate's else-branch).
+            sums.TotalGross = sums.TotalNet;
+            sums.TotalVat   = 0;
+            sums.VatByRate.Clear();
+        }
+
+        session.Sums = sums;
+    }
+
+    /// <summary>
+    /// Renumbers the visible line positions authoritatively (the port of the client-side
+    /// numbering in <c>invSumUpdate</c>): priced lines are numbered sequentially across the whole
+    /// invoice — matching the PDF's <c>Pos.</c> column — while heading/free-text lines
+    /// (<c>typ</c> = "text"/"title") carry no number. The result is written onto each line's
+    /// <c>p</c> field so it flows back to the browser (via the view state) and into the PDF; this
+    /// keeps the online editor and the PDF preview showing the same position numbers, including
+    /// after a reorder.
+    /// </summary>
+    public static void RecomputePositions(InvoiceDraftSession session)
+    {
+        int pos = 0;
+        foreach (var blockTok in session.Req)
+        {
+            if (blockTok is not JObject block || block["itm"] is not JArray lines) continue;
+            foreach (var lineTok in lines)
+            {
+                if (lineTok is not JObject co) continue;
+                string typ = Str(co["typ"]).Trim().ToLowerInvariant();
+                bool numbered = typ is not ("text" or "title");   // only headings/free-text carry no number (mirrors invSumUpdate)
+                co["p"] = numbered ? (JToken)(++pos) : (JToken)"";
+            }
+        }
+    }
+
+    /// <summary>
+    /// Refreshes the draft's plausibility / consistency findings. "error" severity marks
+    /// issues that should block a clean finalise; "warning" is advisory. Kept in German,
+    /// user-readable, so the frontend can render them directly.
+    /// </summary>
+    public static void Validate(InvoiceDraftSession session)
+    {
+        session.ValidationMessages.Clear();
+        void Add(string field, string sev, string msg) =>
+            session.ValidationMessages.Add(new InvoiceDraftValidationMessage(field, sev, msg));
+
+        string email = Str(session.New["invoiceemail"]).Trim();
+        if (email.Length == 0)
+            Add("email", "warning", "Es ist keine E-Mail-Adresse hinterlegt — die Rechnung kann nicht per E-Mail versandt werden.");
+        else if (!IsValidEmail(email))
+            Add("email", "error", "Die E-Mail-Adresse ist ungültig.");
+
+        if (Str(session.New["invoiceaddress"]).Trim().Length == 0)
+            Add("address", "warning", "Es ist keine Rechnungsanschrift hinterlegt.");
+
+        if (!HasAnyItem(session))
+            Add("items", "error", "Die Rechnung enthält keine Positionen.");
+
+        if (!Flag(session.Admin, "p13b"))
+            foreach (var rate in session.Sums.VatByRate.Keys)
+                if (!IsKnownVatRate(rate))
+                    Add("vat", "warning", $"Ungewöhnlicher Umsatzsteuersatz: {rate}%.");
+
+        if (session.Sums.TotalGross < 0)
+            Add("total", "warning", "Der Rechnungsbetrag ist negativ.");
+    }
+
+    // ── helpers ──────────────────────────────────────────────────────────────
+    private static bool HasAnyItem(InvoiceDraftSession session)
+    {
+        foreach (var blockTok in session.Req)
+            if (blockTok is JObject block && block["itm"] is JArray lines && lines.Count > 0)
+                return true;
+        return false;
+    }
+
+    /// <summary>Parses a JToken to a decimal, tolerating German ("12,50") and invariant ("12.50") strings and "%".</summary>
+    internal static decimal Dec(JToken? token)
+    {
+        if (token == null || token.Type == JTokenType.Null) return 0;
+        if (token.Type is JTokenType.Float or JTokenType.Integer) return token.Value<decimal>();
+        return FuchsPdf.ParseDec(Str(token), out decimal d) ? d : 0;
+    }
+
+    private static string Str(JToken? token) =>
+        token == null || token.Type == JTokenType.Null ? "" : token.Type == JTokenType.String ? token.Value<string>() ?? "" : token.ToString();
+
+    private static bool Flag(JObject obj, string key)
+    {
+        var t = obj[key];
+        if (t == null || t.Type == JTokenType.Null) return false;
+        if (t.Type == JTokenType.Boolean) return t.Value<bool>();
+        string s = Str(t).Trim().ToLowerInvariant();
+        return s is "1" or "true" or "yes" or "ja" or "on";
+    }
+
+    /// <summary>Normalises a VAT rate string ("19,0%", "7%", "19") to a canonical numeric string ("19", "7").</summary>
+    internal static string NormalizeRate(string? raw)
+    {
+        string s = (raw ?? "").Replace("%", "").Trim().Replace(',', '.');
+        if (s.Length == 0) return "";
+        if (!double.TryParse(s, NumberStyles.Any, CultureInfo.InvariantCulture, out double d) || d == 0) return "";
+        return d == Math.Floor(d)
+            ? ((long)d).ToString(CultureInfo.InvariantCulture)
+            : d.ToString(CultureInfo.InvariantCulture);
+    }
+
+    private static bool IsKnownVatRate(string rate) => rate is "0" or "7" or "19";
+
+    private static bool IsValidEmail(string email)
+    {
+        int at = email.IndexOf('@');
+        if (at <= 0 || at != email.LastIndexOf('@')) return false;
+        int dot = email.IndexOf('.', at);
+        return dot > at + 1 && dot < email.Length - 1;
+    }
+}

Fuchs/code/InvoiceDraftSession.cs

@@ -0,0 +1,111 @@
+using Newtonsoft.Json.Linq;
+
+namespace Fuchs.intranet;
+
+/// <summary>
+/// Server-side, in-memory editing state for a single invoice draft — the
+/// authoritative source of truth while a back-office user is editing a draft in
+/// the browser (see ADR 0006). The browser is a pure view/input layer: it posts
+/// single changes (<see cref="Fuchs.Services.InvoiceDraftDelta"/>), the server
+/// mutates this session, recomputes totals/VAT (replacing the former client-side
+/// <c>invSumUpdate</c>) and validates, then signals the browser to re-fetch.
+///
+/// This is a <b>data holder</b> only — all calculation, validation, persistence
+/// and rendering live in <see cref="Fuchs.Services.IInvoiceDraftService"/>
+/// (mirroring the <see cref="FdsInvoiceData"/> / <see cref="Fuchs.Services.IInvoiceService"/>
+/// split). The editable payload is kept as the exact JSON shape the editor already
+/// speaks (<c>admin</c> / <c>new</c> / <c>req</c>), so flushing to the DB can reuse
+/// <see cref="Fuchs.Services.IInvoiceService.RegisterInvoiceAsync"/> unchanged.
+/// </summary>
+public sealed class InvoiceDraftSession
+{
+    /// <summary>Opaque per-editor token; also the SignalR group name for targeted signals.</summary>
+    public string Token { get; init; } = "";
+
+    /// <summary>Owning user account id (drafts are single-user; used for auth + events).</summary>
+    public string UserAccountId { get; init; } = "";
+
+    /// <summary>DB invoice id once the session has been flushed (Zwischenspeichern); empty while cache-only.</summary>
+    public string InvId { get; set; } = "";
+
+    /// <summary>Always true here — sessions only ever hold unfinalised drafts.</summary>
+    public bool IsDraft { get; set; } = true;
+
+    /// <summary>Bumped on every applied mutation; the browser refetches when the signalled version changes.</summary>
+    public int Version { get; set; }
+
+    /// <summary>UTC of the last read/write; drives the idle sliding-TTL and expiry warnings.</summary>
+    public DateTime LastAccessUtc { get; set; } = DateTime.UtcNow;
+
+    /// <summary>Guards against sending more than one expiry warning per idle window.</summary>
+    public bool ExpiryWarningSent { get; set; }
+
+    // ── Editable payload (exact editor JSON shape) ───────────────────────────
+    /// <summary>Header/admin flags: type, customerid, p13b, setmode, paymentterms…</summary>
+    public JObject Admin { get; set; } = new();
+
+    /// <summary>Recipient/new fields: title/invoicetitle, invoiceaddress, invoiceemail, provisionlocation/-period, CustomValues…</summary>
+    public JObject New { get; set; } = new();
+
+    /// <summary>Service-request blocks; each block is a JObject with an <c>items</c> JArray (the line items).</summary>
+    public JArray Req { get; set; } = new();
+
+    // ── Computed (by the draft service; never trusted from the client) ───────
+    /// <summary>Server-computed totals/VAT — the values the client used to compute in <c>invSumUpdate</c>.</summary>
+    public InvoiceDraftSums Sums { get; set; } = new();
+
+    /// <summary>Plausibility / consistency results, refreshed on every recompute.</summary>
+    public List<InvoiceDraftValidationMessage> ValidationMessages { get; } = new();
+
+    /// <summary>Automatic change history, appended on every applied patch. Cache-only (never persisted).</summary>
+    public List<ChangeHistoryEntry> History { get; } = new();
+
+    public void Touch() => LastAccessUtc = DateTime.UtcNow;
+}
+
+/// <summary>Server-computed invoice totals — the authoritative replacement for the browser's <c>sms</c> object.</summary>
+public sealed class InvoiceDraftSums
+{
+    /// <summary>Total net (<c>ttn</c>).</summary>
+    public decimal TotalNet { get; set; }
+    /// <summary>Total gross (<c>ttb</c>); equals net when §13b reverse-charge is active.</summary>
+    public decimal TotalGross { get; set; }
+    /// <summary>Total VAT (<c>ttvat</c>).</summary>
+    public decimal TotalVat { get; set; }
+    /// <summary>Service net (<c>tscn</c>) — the service-refund base.</summary>
+    public decimal ServiceNet { get; set; }
+    /// <summary>Service VAT (<c>tscvat</c>).</summary>
+    public decimal ServiceVat { get; set; }
+    /// <summary>VAT amount per rate string (e.g. "19" → 123.45), matching the editor's <c>sms.vat</c> map.</summary>
+    public Dictionary<string, decimal> VatByRate { get; } = new();
+    /// <summary>Net per block, keyed by block id — feeds the per-block sub-sum row.</summary>
+    public Dictionary<string, decimal> NetByBlock { get; } = new();
+}
+
+/// <summary>A single plausibility/consistency finding for the draft.</summary>
+/// <param name="Field">Logical field the message relates to (e.g. "email", "address", "items").</param>
+/// <param name="Severity">"error" blocks a clean finalise; "warning"/"info" are advisory.</param>
+/// <param name="Message">German, user-readable text.</param>
+public readonly record struct InvoiceDraftValidationMessage(string Field, string Severity, string Message);
+
+/// <summary>
+/// One automatically-recorded change in the draft's history (shown in the
+/// "Änderungshistorie" dialog). Captured on every applied patch; lives only for
+/// the cache lifetime of the session and is never persisted to the database.
+/// </summary>
+public sealed class ChangeHistoryEntry
+{
+    public DateTime TimestampUtc { get; init; } = DateTime.UtcNow;
+    /// <summary>User account id that made the change.</summary>
+    public string UserAccountId { get; init; } = "";
+    /// <summary>The change target/op as sent by the editor (e.g. "item.qty", "email", "p13b").</summary>
+    public string Target { get; init; } = "";
+    /// <summary>Optional item/block id the change applied to.</summary>
+    public string Ref { get; init; } = "";
+    /// <summary>Previous value, stringified for display (may be empty).</summary>
+    public string OldValue { get; init; } = "";
+    /// <summary>New value, stringified for display (may be empty).</summary>
+    public string NewValue { get; init; } = "";
+    /// <summary>Version the session reached after applying this change.</summary>
+    public int Version { get; init; }
+}

Fuchs/code/ReminderDraftCalculator.cs

@@ -0,0 +1,92 @@
+using System.Globalization;
+using Newtonsoft.Json.Linq;
+
+namespace Fuchs.intranet;
+
+/// <summary>
+/// Server-side, pure aggregation of a reminder draft's open amount — the authoritative
+/// replacement for the browser's inline figure (ADR 0006, mirroring
+/// <see cref="InvoiceDraftCalculator"/>). The user's requirement is that the computed
+/// figure lives in the backend cache, not the frontend.
+///
+/// A reminder chases a single invoiced amount: <c>AmountOpen = AmountTotal - AmountPayed</c>
+/// (both read from the editor's <c>new</c> block). Static/pure, hence exhaustively
+/// unit-testable.
+/// </summary>
+public static class ReminderDraftCalculator
+{
+    /// <summary>Recomputes the reminder's open amount from the edited <c>amount</c> / <c>amount_payed</c>.</summary>
+    public static void RecomputeTotals(ReminderDraftSession session)
+    {
+        decimal total = Dec(session.New["amount"]);
+        decimal payed = Dec(session.New["amount_payed"]);
+        session.Sums = new ReminderDraftSums
+        {
+            AmountTotal = total,
+            AmountPayed = payed,
+            AmountOpen  = total - payed
+        };
+    }
+
+    /// <summary>
+    /// Refreshes the draft's plausibility / consistency findings. "error" severity marks
+    /// issues that should block a clean finalise; "warning" is advisory. Kept in German,
+    /// user-readable, so the frontend can render them directly.
+    /// </summary>
+    public static void Validate(ReminderDraftSession session)
+    {
+        session.ValidationMessages.Clear();
+        void Add(string field, string sev, string msg) =>
+            session.ValidationMessages.Add(new ReminderDraftValidationMessage(field, sev, msg));
+
+        string email = Str(session.New["invoiceemail"]).Trim();
+        if (email.Length == 0)
+            Add("email", "warning", "Es ist keine E-Mail-Adresse hinterlegt — die Mahnung kann nicht per E-Mail versandt werden.");
+        else if (!IsValidEmail(email))
+            Add("email", "error", "Die E-Mail-Adresse ist ungültig.");
+
+        if (Str(session.New["invoiceaddress"]).Trim().Length == 0)
+            Add("address", "warning", "Es ist keine Anschrift hinterlegt.");
+
+        if (Str(session.New["subject"]).Trim().Length == 0)
+            Add("subject", "warning", "Es ist kein Betreff hinterlegt.");
+
+        if (session.Sums.AmountOpen <= 0)
+            Add("amount", "warning", "Der offene Betrag ist null oder negativ — es besteht keine offene Forderung.");
+    }
+
+    // ── helpers ──────────────────────────────────────────────────────────────
+    /// <summary>Parses a JToken to a decimal, tolerating German ("12,50" / "1.234,56") and invariant ("12.50") strings.</summary>
+    internal static decimal Dec(JToken? token)
+    {
+        if (token == null || token.Type == JTokenType.Null) return 0;
+        if (token.Type is JTokenType.Float or JTokenType.Integer) return token.Value<decimal>();
+        return ParseAmount(Str(token));
+    }
+
+    /// <summary>
+    /// Parses a currency string, resolving the German/invariant ambiguity: a value with both
+    /// separators treats "." as thousands and "," as decimal ("1.234,56"); a value with only ","
+    /// treats it as the decimal separator ("12,50"); otherwise it is parsed invariant ("1234.56").
+    /// </summary>
+    internal static decimal ParseAmount(string? raw)
+    {
+        string s = (raw ?? "").Trim();
+        if (s.Length == 0) return 0;
+        bool hasComma = s.Contains(','), hasDot = s.Contains('.');
+        if (hasComma && hasDot) s = s.Replace(".", "").Replace(',', '.');   // German "1.234,56"
+        else if (hasComma)      s = s.Replace(',', '.');                    // German "12,50"
+        return decimal.TryParse(s, NumberStyles.Any, CultureInfo.InvariantCulture, out decimal d) ? d : 0;
+    }
+
+    private static string Str(JToken? token) =>
+        token == null || token.Type == JTokenType.Null ? "" : token.Type == JTokenType.String ? token.Value<string>() ?? "" : token.ToString();
+
+    private static bool IsValidEmail(string email)
+    {
+        int at = email.IndexOf('@');
+        if (at <= 0 || at != email.LastIndexOf('@')) return false;
+        int dot = email.IndexOf('.', at);
+        return dot > at + 1 && dot < email.Length - 1;
+    }
+}

Fuchs/code/ReminderDraftSession.cs

@@ -0,0 +1,81 @@
+using Newtonsoft.Json.Linq;
+
+namespace Fuchs.intranet;
+
+/// <summary>
+/// Server-side, in-memory editing state for a single reminder (Zahlungserinnerung)
+/// draft — the authoritative source of truth while a back-office user edits a draft in
+/// the browser. This mirrors <see cref="InvoiceDraftSession"/> for reminders (ADR 0006):
+/// the browser is a pure view/input layer that posts single changes
+/// (<see cref="Fuchs.Services.ReminderDraftDelta"/>); the server mutates this session,
+/// recomputes the open amount and validates, then signals the browser to re-fetch.
+///
+/// This is a <b>data holder</b> only — all calculation, validation, persistence and
+/// rendering live in <see cref="Fuchs.Services.IReminderDraftService"/> (mirroring the
+/// <see cref="FdsReminderData"/> / <see cref="Fuchs.Services.IReminderService"/> split).
+/// The editable payload is kept as the exact JSON shape the editor already speaks
+/// (<c>new</c> / <c>rem</c>), so flushing to the DB can reuse
+/// <see cref="Fuchs.Services.IReminderService.RegisterReminderAsync"/> unchanged.
+/// The change-history record type (<see cref="ChangeHistoryEntry"/>) is shared with the
+/// invoice draft; validation messages use the reminder-specific
+/// <see cref="ReminderDraftValidationMessage"/>.
+/// </summary>
+public sealed class ReminderDraftSession
+{
+    /// <summary>Opaque per-editor token; also the SignalR group name for targeted signals.</summary>
+    public string Token { get; init; } = "";
+
+    /// <summary>Owning user account id (drafts are single-user; used for auth + events).</summary>
+    public string UserAccountId { get; init; } = "";
+
+    /// <summary>DB reminder id once the session has been flushed (Zwischenspeichern); empty while cache-only.</summary>
+    public string RemId { get; set; } = "";
+
+    /// <summary>Always true here — sessions only ever hold unfinalised drafts.</summary>
+    public bool IsDraft { get; set; } = true;
+
+    /// <summary>Bumped on every applied mutation; the browser refetches when the signalled version changes.</summary>
+    public int Version { get; set; }
+
+    /// <summary>UTC of the last read/write; drives the idle sliding-TTL and expiry warnings.</summary>
+    public DateTime LastAccessUtc { get; set; } = DateTime.UtcNow;
+
+    /// <summary>Guards against sending more than one expiry warning per idle window.</summary>
+    public bool ExpiryWarningSent { get; set; }
+
+    // ── Editable payload (exact editor JSON shape) ───────────────────────────
+    /// <summary>Recipient/new fields: subject, invoiceaddress, invoiceemail, text, amount, amount_payed, CustomValues…</summary>
+    public JObject New { get; set; } = new();
+
+    /// <summary>Reference fields: invid, type, level, invoiceid, invoicedate, sender…</summary>
+    public JObject Rem { get; set; } = new();
+
+    // ── Computed (by the draft service; never trusted from the client) ───────
+    /// <summary>Server-computed open-amount aggregation — the values the client used to compute inline.</summary>
+    public ReminderDraftSums Sums { get; set; } = new();
+
+    /// <summary>Plausibility / consistency results, refreshed on every recompute.</summary>
+    public List<ReminderDraftValidationMessage> ValidationMessages { get; } = new();
+
+    /// <summary>Automatic change history, appended on every applied patch. Cache-only (never persisted).</summary>
+    public List<ChangeHistoryEntry> History { get; } = new();
+
+    public void Touch() => LastAccessUtc = DateTime.UtcNow;
+}
+
+/// <summary>Server-computed reminder totals — the authoritative open-amount for the draft.</summary>
+public sealed class ReminderDraftSums
+{
+    /// <summary>Invoiced amount (gross) the reminder chases.</summary>
+    public decimal AmountTotal { get; set; }
+    /// <summary>Amount already paid against the invoice.</summary>
+    public decimal AmountPayed { get; set; }
+    /// <summary>Still-open amount (<c>AmountTotal - AmountPayed</c>) — the reminder's headline figure.</summary>
+    public decimal AmountOpen { get; set; }
+}
+
+/// <summary>A single plausibility/consistency finding for the reminder draft.</summary>
+/// <param name="Field">Logical field the message relates to (e.g. "email", "address", "amount").</param>
+/// <param name="Severity">"error" blocks a clean finalise; "warning"/"info" are advisory.</param>
+/// <param name="Message">German, user-readable text.</param>
+public readonly record struct ReminderDraftValidationMessage(string Field, string Severity, string Message);

Fuchs/js/intranet/fis_main.js

@@ -284,3 +284,65 @@ $fis.notifications = {
         }, 9000);
     }
 };
+
+/* Live draft-editing client (ADR 0006/0007). Separate SignalR connection to the
+   dedicated /draftpreview hub; the server signals the *one* browser editing a draft
+   (group = session token) to re-fetch (draftReady), warns before idle expiry
+   (draftExpiring), and tells it to close on eviction (draftClosed). The editor
+   (fis.inv_shared.js) registers the open draft via $fis.draft.bind(token, {...}). */
+$fis.draft = {
+    connection: null,
+    active: null,   /* { token, onReady(version), onExpiring(secondsLeft), onClosed(reason) } */
+    init: function () {
+        if (typeof signalR === 'undefined' || this.connection !== null || !$ocms.auth.useraccount_id) {
+            return;
+        }
+        this.connection = new signalR.HubConnectionBuilder()
+            .withUrl('/draftpreview')
+            .withAutomaticReconnect()
+            .build();
+        this.connection.on('draftReady',    (p) => this._dispatch('onReady',    p, (p) => p.version));
+        this.connection.on('draftExpiring', (p) => this._dispatch('onExpiring', p, (p) => p.secondsLeft));
+        this.connection.on('draftClosed',   (p) => this._dispatch('onClosed',   p, (p) => p.reason));
+        /* Re-join the active draft's group after a (re)connect — group membership is
+           per-connection and is lost when the socket drops. */
+        this.connection.onreconnected(() => { if (this.active) { this._invoke('JoinDraft', this.active.token); } });
+        this.connection.onclose(() => {
+            console.warn('Draft connection closed; retrying in 5s.');
+            this.connection = null;
+            setTimeout(() => { this.init(); if (this.active) { this.bind(this.active.token, this.active); } }, 5000);
+        });
+        this.start();
+    },
+    start: function () {
+        this.connection.start()
+            .then(() => { if (this.active) { this._invoke('JoinDraft', this.active.token); } })
+            .catch((err) => {
+                console.warn('Draft connection failed to start; retrying in 5s.', err);
+                this.connection = null;
+                setTimeout(() => this.init(), 5000);
+            });
+    },
+    /* Registers the currently open draft and joins its signal group. handlers:
+       { onReady, onExpiring, onClosed }. */
+    bind: function (token, handlers) {
+        if (!token) { return; }
+        this.active = $.extend({ token: token }, handlers || {});
+        if (this.connection === null) { this.init(); }
+        this._invoke('JoinDraft', token);
+    },
+    /* Unregisters + leaves the group (editor closed). */
+    release: function (token) {
+        if (this.active && (!token || this.active.token === token)) { this.active = null; }
+        this._invoke('LeaveDraft', token);
+    },
+    _invoke: function (method, token) {
+        if (!token || !this.connection || this.connection.state !== 'Connected') { return; }
+        this.connection.invoke(method, token).catch((err) => console.warn('Draft ' + method + ' failed', err));
+    },
+    _dispatch: function (handler, payload, argOf) {
+        payload = payload || {};
+        if (!this.active || this.active.token !== payload.token) { return; }
+        if (typeof this.active[handler] === 'function') { this.active[handler](argOf(payload)); }
+    }
+};

Fuchs/js/intranet/fis_main_go.js

@@ -1,4 +1,5 @@
 $(document).ready(function () {
     $fis.notifications.init();
+    $fis.draft.init();
     $fis.ov();
 });

Fuchs/js/intranet/modules/fis.inv_shared.js

@@ -99,11 +99,375 @@ $inv.eM = (r, re, opt) => {
     if ((opt || '').split(',').includes('setm') === true) {
         m.push({ lbl: $ict.setm, fnc: $inv.ssetmode });
     }
+    if ((opt || '').split(',').includes('iss') === true) {  /* backend-authoritative draft (ADR 0006) */
+        m.push({ lbl: 'Änderungshistorie', fnc: () => $inv.d.history() });
+        m.push({ lbl: 'Änderungen verwerfen', fnc: () => $inv.d.discard() });
+    }
     if (booln(r, false) === true) {
         m.push({ lbl: $ict.rel, fnc: $inv.rReload });
     }
     return $('#topbar').ocmsmenu(m);  /* empty Array => empty menu */
 };
+/* ── Backend-authoritative draft editing controller (ADR 0006/0007) ───────────
+   The server holds the truth for an invoice draft in an in-memory session; this
+   object seeds it, sends single edits as deltas, and renders the totals footer +
+   validation from the authoritative server state. It is invoice-only: reminders
+   never obtain a token (invSumUpdate, the seed trigger, is only bound for invoices),
+   so they keep the legacy stateless flow untouched. */
+$inv.d = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.d.tbl().data('dtoken') || ''; },
+    /* Hash each assembled block so only genuinely-changed blocks are sent as deltas. */
+    hashes: function () {
+        let bai = $inv.d.tbl().data('bai') || [], h = {};
+        $.each(bai, (i, b) => { h[(b.Id || '').toString()] = JSON.stringify(b); });
+        return h;
+    },
+    /* Seed the authoritative server session from the assembled editor payload. Called
+       once from invSumUpdate on open; thereafter the backend is the source of truth. */
+    seed: function (payload) {
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.d.tbl().data('dtoken', r.token).data('dver', r.version).data('dhashes', $inv.d.hashes()).data('dorder', $inv.d.order());
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.d.refresh(),
+                    onExpiring: (s) => $inv.d.warnExpiry(s),
+                    onClosed: (reason) => $inv.d.closed(reason)
+                });
+                $inv.d.refresh();
+            }, error: () => { l.rC('freeze'); }, complete: () => { $inv.d.tbl().removeData('dseeding'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the totals footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dstate'), data: { token: t }, success: (state) => {
+                $inv.d.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } },
+            complete: () => { $inv.d.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.d.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('dver', state.version).data('serverSums', state.sums);
+        $inv.d.footer(tbl, state.sums || {}, state.admin || {});
+        $inv.d.validation(state.validation || []);
+        $inv.d.applyPositions(tbl, state.req || []);
+    },
+    /* Push the server's authoritative position numbers back onto the rendered rows so the online
+       editor and the PDF preview always agree (the server numbers priced lines continuously; the
+       browser must not keep its own numbering). Only the position cell is touched — no re-render. */
+    applyPositions: function (tbl, req) {
+        (req || []).forEach((b) => (b && b.itm || []).forEach((co) => {
+            if (!co || (co.id || '') === '') { return; }
+            let cell = tbl.find('#itm' + co.id + ' td.keep').first();
+            if (cell.length) { cell.text(co.p != null ? co.p : ''); }
+        }));
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $inv.d.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.d.refresh(); },
+            error: (xhr) => { $inv.d.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } }
+        });
+    },
+    /* The current section id sequence (used to detect a reorder that changes no block content). */
+    order: function () { return (($inv.d.tbl().data('bai')) || []).map((b) => (b.Id || '').toString()); },
+    /* Diff the freshly-rebuilt blocks against the last-synced state and send only the
+       changed/removed blocks as granular block.replace / block.remove deltas. A pure section
+       reorder (same blocks, new sequence) changes no block hash, so it is sent separately as a
+       block.order delta; the server reorders the cache, renumbers positions and pushes them back. */
+    syncChanged: function (tbl) {
+        if (($inv.d.token()) === '') { return; }
+        let bai = tbl.data('bai') || [], prev = tbl.data('dhashes') || {}, next = {}, changed = [], removed = [];
+        $.each(bai, (i, b) => { let id = (b.Id || '').toString(), h = JSON.stringify(b); next[id] = h; if (prev[id] !== h) { changed.push(b); } });
+        $.each(prev, (id) => { if (next[id] === undefined) { removed.push(id); } });
+        let order = $inv.d.order(), prevOrder = tbl.data('dorder') || [];
+        tbl.data('dhashes', next).data('dorder', order);
+        changed.forEach((b) => $inv.d.sync({ Target: 'block.replace', Ref: (b.Id || '').toString(), Value: b }));
+        removed.forEach((id) => $inv.d.sync({ Target: 'block.remove', Ref: id }));
+        let sameSet = prevOrder.length === order.length && prevOrder.slice().sort().join(',') === order.slice().sort().join(',');
+        if (sameSet && prevOrder.join(',') !== order.join(',')) { $inv.d.sync({ Target: 'block.order', Value: order }); }
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.d.token() === '') { return; }
+        let map = { invoicetitle: 'title', invoiceaddress: 'address', invoiceemail: 'email', loc: 'provisionlocation', provisionlocation: 'provisionlocation', provisionperiod: 'provisionperiod' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.d.sync({ Target: target, Value: val });
+    },
+    /* Render the totals footer from the server sums (port of invSumUpdate's footer half). */
+    footer: function (tbl, sums, admin) {
+        let ft = tbl.children('tfoot').empty(); tbl.nextAll('.fnote').remove();
+        let p13b = bool(admin.p13b, false);
+        let rwcy = (lbl, val, cls) => $$.tdc('currency', $$.tr(ft, { class: cls || 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 4 }).text(lbl)]), fnum(val, $rct.cst));
+        let fn = (t) => $$.dc('fnote').insertAfter(tbl).rwText(t);
+        rwcy('Netto', sums.total_net || 0);
+        if (p13b === false) { $.each(sums.vat || {}, (rate, amt) => rwcy($rct.vat + ' ' + rate + '%', amt, 'tvat')); }
+        rwcy('Summe', sums.total_gross || 0);
+        let itype = (admin.type || '');
+        if (itype === 'i') { fn($rct.note2); fn($rct.note4); }
+        else if (itype === 'c') { fn($rct.note2); }
+        else {
+            fn(string($rct.note3, [fnum(((sums.service_net || 0) + (sums.service_vat || 0)) * (admin.tax_servicerefund || 0), $rct.cst)])).aC('ntax');
+            fn($rct.note2);
+            fn(string($rct.note1, [fnum((sums.service_net || 0) + (sums.service_vat || 0), $rct.cst), fnum(sums.service_net || 0, $rct.cst), fnum(sums.service_vat || 0, $rct.cst)]));
+        }
+        if (p13b === true) { fn($rct.note13b); }
+    },
+    validation: function (msgs) {
+        let frm = $('div.invoice_layout'); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise, cancel = discard. */
+    preview: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout();
+        let email = ($inv.d.tbl().data('new') || {}).invoiceemail || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), total = response.total;
+                if (total > 10) { $$.dc('note warn', c).text($ict.tpe); }
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                for (let ic = (response.img || []).length + 1; ic <= total; ic++) { $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna)); }
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('inv/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('req/sconf'), data: { id: sv.invid }, success: (cresp) => {
+                                        ct.trigger('modal_close');
+                                        if (cresp.hasFile === true) { window.open($ocms.url('req/idoc') + '?id=' + sv.invid, '_blank'); }
+                                        $inv.d.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.d.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dsave'), data: { token: t }, success: (r) => { $inv.d.tbl().data('invid', r.invid); },
+            error: () => { alert($ict.eis); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    discard: function () {
+        let invid = $inv.d.tbl().data('invid') || '';
+        if (invid === '') { alert('Es wurde noch kein Zwischenstand gespeichert, der wiederhergestellt werden könnte.'); return; }
+        if (confirm('Alle Änderungen verwerfen und den zuletzt gespeicherten Stand neu laden?') === false) { return; }
+        $inv.d.close();
+        $inv.cntInv({ id: invid });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Rechnungsentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.d.token();
+        $inv.d.tbl().removeData('dtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Rechnungsentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Rechnungsentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.d.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('inv/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.d.tbl().removeData('dtoken');
+    }
+};
+/* ── Backend-authoritative reminder draft editing (ADR 0006/0007) ─────────────
+   The reminder mirror of $inv.d: the server holds the truth for a reminder draft in
+   an in-memory session; this object seeds it (rem/dopen), sends single edits as deltas
+   (rem/dpatch), and renders the open-amount footer + validation from the authoritative
+   server state (rem/dstate). Preview renders straight from the cache (rem/dpreview);
+   confirm flushes (rem/dsave) then finalises + emails (rem/conf). It coexists with $inv.d
+   on the same DOM: each keys off its own token (rdtoken vs dtoken), so the shared inline
+   editor safely no-ops for the mode that is not active. */
+$inv.rd = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.rd.tbl().data('rdtoken') || ''; },
+    /* Seed the authoritative server session from the assembled reminder editor payload. */
+    seed: function (payload) {
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.rd.tbl().data('rdtoken', r.token).data('rdver', r.version);
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.rd.refresh(),
+                    onExpiring: (s) => $inv.rd.warnExpiry(s),
+                    onClosed: (reason) => $inv.rd.closed(reason)
+                });
+                $inv.rd.refresh();
+            }, error: () => { l.rC('freeze'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the open-amount footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dstate'), data: { token: t }, success: (state) => {
+                $inv.rd.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } },
+            complete: () => { $inv.rd.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.rd.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('rdver', state.version).data('serverSums', state.sums).data('remid', state.remid || '');
+        $inv.rd.footer(tbl, state.sums || {});
+        $inv.rd.validation(state.validation || []);
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $inv.rd.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.rd.refresh(); },
+            error: (xhr) => { $inv.rd.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } }
+        });
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.rd.token() === '') { return; }
+        let map = { subject: 'subject', invoiceaddress: 'address', invoiceemail: 'email', text: 'text' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.rd.sync({ Target: target, Value: val });
+    },
+    /* Amount / amount-paid come from the item-row dialog; send both as their own deltas. */
+    syncAmount: function (amount, amount_payed) {
+        if ($inv.rd.token() === '') { return; }
+        $inv.rd.sync({ Target: 'amount', Value: (amount != null ? amount : 0).toString() });
+        $inv.rd.sync({ Target: 'amount_payed', Value: (amount_payed != null ? amount_payed : 0).toString() });
+    },
+    /* Render the open-amount footer from the server sums. */
+    footer: function (tbl, sums) {
+        let ft = tbl.children('tfoot').empty();
+        let tr = $$.tr(ft, { class: 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 3 }).text('Offener Betrag')]);
+        $$.tdc('currency', tr, fnum(sums.amount_open || 0, $rct.cst));
+    },
+    validation: function (msgs) {
+        let frm = $inv.rd.layout(); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise + email, cancel = discard. */
+    preview: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout();
+        let email = (($inv.rd.tbl().data('new') || {}).invoiceemail) || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88);
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('rem/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('rem/conf'), data: { id: sv.remid }, success: () => {
+                                        ct.trigger('modal_close');
+                                        window.open($ocms.url('rem/idoc') + '?id=' + sv.remid, '_blank');
+                                        $inv.rd.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($t.f1); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.rd.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($t.f1); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dsave'), data: { token: t }, success: (r) => { $inv.rd.tbl().data('remid', r.remid); },
+            error: () => { alert($t.f1); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Mahnentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.rd.token();
+        $inv.rd.tbl().removeData('rdtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Mahnentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Mahnentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.rd.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('rem/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.rd.tbl().removeData('rdtoken');
+    }
+};
 $inv.cInv2 = function (data) {
     let fr = $$.dc('rfrm').ldng(1);
     let o = $ocms.dlg(fr, { width: 1000 });
@@ -481,9 +845,12 @@ $inv.cSt = function (data) {
 };
 $inv.eHtml = function (ev) {
     let t = $(this), frmct = ev.data instanceof jQuery ? ev.data : ev.data.t;
-    /* invoiceemail must stay plain text — using the TinyMCE/html editor here used to wrap the
+    /* Single-line fields must stay plain text — the TinyMCE/html editor wraps the value in <p>
-       address in <p> tags, which then got posted and persisted verbatim into SendToEmail. */
+       tags, which used to get posted and persisted verbatim (e.g. <p>18.06.2026</p> in the
-    let isPlainText = ev.data.nme === 'invoiceemail';
+       Leistungsdatum). The backend sanitises HTML too (single source of truth, ADR 0006), but
+       keeping these plain here avoids the UI briefly holding the wrapped value. Multi-line fields
+       (invoiceaddress, loc) stay HTML-capable and are normalised to newlines server-side. */
+    let isPlainText = ['invoiceemail', 'provisionperiod', 'invoicetitle'].includes(ev.data.nme);
     let flds = isPlainText
         ? [{ name: 'txt', label: 'Text', type: 'text', value: frmct.text() }]
         : [{ name: 'txt', label: 'Text', type: 'html', value: frmct.html(), tinymce: true, attr: { style: 'height: 300px' } }];
@@ -499,6 +866,11 @@ $inv.eHtml = function (ev) {
             if (typeof change === 'function') {
                 change(response.txt);
             }
+            /* backend-authoritative: mirror the inline recipient-field edit to the server session.
+               Invoice and reminder editors share this DOM; each syncField no-ops unless its own
+               draft token is present, so only the active mode's session receives the delta. */
+            $inv.d.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
+            $inv.rd.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
         },
         tinymce: { valid_elements: 'br', hidemenu: true, hidetoolbar: true }
     }
@@ -584,7 +956,11 @@ $inv.eRw = function(row, dta, flds) {
         }, typedvalues: true
     });
 };
-$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', swapdone: (p1, p2, i1, i2) => { $inv.t_fds_inv(); } }) }
+/* Reorder items via drag. The DOM swap happens inside the Sortable during the drag; we commit
+   the new order once, reliably, on drop (onend) — that recomputes positions/totals and pushes the
+   changed block(s) to the backend session (t_fds_inv -> syncChanged). Committing on drop (rather
+   than on every mid-drag hover-swap) avoids rebuilding the row that is currently being dragged. */
+$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', onend: () => { $inv.t_fds_inv(); } }) }
 $inv.rrw = function () {
     let rw = $(this), dta = rw.data(), co = {}, ph = rw.is('.placeholder'), hn = rw.is('.hidenote');
     let oHtml = (e) => $$.d().append(e).html();
@@ -713,6 +1089,13 @@ $inv.invSumUpdate = function () {
     }
     tbl.data('sms', sms);
     tbl.data('bai', ba);
+    /* Backend-authoritative seeding (ADR 0006): on the first calculation of an invoice
+       draft (invSumUpdate is only bound for invoices, never reminders), hand the assembled
+       model to the server session and switch to server-driven totals from then on. */
+    if ((tbl.data('dtoken') || '') === '' && bool(tbl.data('dseeding'), false) === false && ((tbl.data('admin') || {}).type != null)) {
+        tbl.data('dseeding', true);
+        $inv.d.seed($.extend($inv.invcPayload(tbl.data()), { invid: tbl.data('invid') || '' }));
+    }
 };
 $inv.worknotes = function (rx) {
     let wn = '';
@@ -800,7 +1183,13 @@ $inv.rendersrq = function () {
         $$.tdc('currency isumval', istr);
     }
 };
-$inv.t_fds_inv = () => { $('div.invoice_layout table.invi').trigger('fds.inv'); };
+$inv.t_fds_inv = () => {
+    let tbl = $('div.invoice_layout table.invi');
+    tbl.trigger('fds.inv');
+    /* After any local item mutation, push the changed block(s) to the authoritative
+       server session as granular deltas (invoice drafts only — reminders have no token). */
+    if ((tbl.data('dtoken') || '') !== '') { $inv.d.syncChanged(tbl); }
+};
 $inv.sedit = () => {
     $inv.sprev(true);
 };
@@ -855,6 +1244,7 @@ $inv.sp13b = () => {
     } else {
     }
     tbl.trigger('fds.inv');
+    $inv.d.sync({ Target: 'p13b', Value: d.admin.p13b });
 };
 /* Maps an item row's data to the backend item contract consumed by InvoiceSetPricing
    / FuchsPdf.ApplyInvoice: { id, type, title (plain), desc (html), qty, price_net,
@@ -909,6 +1299,7 @@ $inv.setSetmode = (mode) => {
     let opts = (d.inv.InvoiceOptions || '').split(',').filter(x => x !== '' && x.indexOf('setmode:') !== 0);
     if (mode && mode !== 'setprice') { opts.push('setmode:' + mode); }
     d.inv.InvoiceOptions = opts.join(',');
+    $inv.d.sync({ Target: 'setmode', Value: mode });
 };
 $inv.sctp = () => {
     let flds = $invcol.ctp;
@@ -925,6 +1316,7 @@ $inv.sctp = () => {
             cvo.contactEmail = response.email;
             d.new.CustomValues = JSON.stringify(cvo);  //Assign it to new Values so that this is submitted also
             l.find('.ctpfrm').text(ne(response.name, response.email));
+            $inv.d.sync({ Target: 'contact', Value: { name: response.name, email: response.email } });
 
         }, typedvalues: true
     });
@@ -949,82 +1341,12 @@ $inv.invcPayload = function (d) {
     adm.customerid = (adm.customerid != null ? adm.customerid : adm.CustomerId);
     return { admin: adm, req: d.bai, sms: d.sms, new: nw };
 };
-$inv.ssave = () => {
+/* Zwischenspeichern and preview now run against the backend-authoritative session
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
+   (ADR 0006): no full-invoice re-upload — the cached draft is flushed / rendered by
-    $inv.t_fds_inv();
+   token. See $inv.d.save / $inv.d.preview. The finalise + email path (req/sconf) is
-    l.aC('freeze');
+   unchanged and is invoked from the preview modal's confirm handler. */
-    $ocms.postXT({
+$inv.ssave = () => { $inv.d.save(); };
-        url: $ocms.url('req/save'), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid || '' }, success: (response) => {
+$inv.sprev = (change) => { $inv.d.preview(); };
-            $inv.cntInv({ id: response.id });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
-$inv.sprev = (change) => {
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
-    change = bool(change, false);
-    $inv.t_fds_inv();
-    l.aC('freeze');
-    //console.debug({ admin: d.admin, req: d.bai, sms: d.sms, new: d.new });
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc),false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('req/' + (change === true ?'sedit':'sprep')), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid ||'' }, success: (response) => {
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), invid = response.id, invtp = response.total;
-            if (invtp > 10) {
-                $$.dc('note warn', c).text($ict.tpe);
-            }
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            for (let ic = (response.img || []).length + 1; ic <= invtp; ic++) {
-                $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna));
-            }
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI, confirm: function (e) {
-                    let ct = $(this);
-                    l.aC('freeze');  /* spinner while the invoice is finalized/emailed on the backend */
-                    $ocms.postXT({
-                        url: $ocms.url('req/sconf'), data: { id: invid }, success: (cresp) => {
-                            ct.trigger('modal_close');
-                            if (cresp.hasFile === true) {
-                                window.open($ocms.url('req/idoc') + '?id=' + invid, '_blank');  /* open pdf in new tab, only if a file was actually created */
-                            }
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }, complete: () => {
-                            l.rC('freeze');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('req/sdel'), data: {
-                                id: invid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
 $inv.rReload = () => {
     try {
         let s = $('#listframe ul.rql:first').data();
@@ -1203,6 +1525,8 @@ $inv.eRowR = function (ev) {
             $.extend(tdta.rm, res);
             tbl.data(tdta);
             $inv.rRemRw.call(row, tdta);
+            /* backend-authoritative: mirror the edited amount / amount-paid to the server session */
+            $inv.rd.syncAmount(tdta.rm.amount, tdta.rm.amount_payed);
         }, typedvalues: true
     });
 };
@@ -1243,57 +1567,26 @@ $inv.ccRem_s2 = function (id, sets) {  //reminder creation
             rif.tbl.children('tbody').each($inv.bdysort);
             rif.tbl.trigger('fds.inv');  /* trigger calculations */
 
+            /* Seed the authoritative server session (ADR 0006). Amounts join the recipient
+               fields in the 'new' block; the reference invoice data goes into 'rem'. From here
+               the backend owns the open-amount computation and validation; inline edits and the
+               item-row dialog post single deltas (see $inv.rd). */
+            let nw = rif.tbl.data('new');
+            nw.amount = rem.amount; nw.amount_payed = rem.amount_payed;
+            $inv.rd.seed({
+                rem: { invid: rem.invid, type: rem.type, invoiceid: rem.invoiceid, invoicedate: rem.invoicedate },
+                new: nw
+            });
         }, complete: () => {
             //o.c.trigger('modal_close');
         }
     });
 };
 $inv.rprev = () => {
-    var l = $('div.invoice_layout'), tbl = l.find('table.invi'), d = tbl.data();
+    /* Preview + finalise now run through the backend-authoritative session ($inv.rd):
-    $.extend(d.new, tbl.find('tbody > tr:first').data());
+       the PDF renders straight from the server cache (no rem/prep DB write), and confirm
-    l.aC('freeze');
+       flushes (rem/dsave) then finalises + emails (rem/conf). */
-    //console.debug({ rem: d.rm, new: d.new });
+    $inv.rd.preview();
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('rem/prep'), data: { remc: JSON.stringify({ rem: d.rm, new: d.new }), id: d.invid || '' }, success: (response) => {
-            l.rC('freeze');
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), remid = response.id;
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd, confirm: function (e) {
-                    let ct = $(this);
-                    $ocms.postXT({
-                        url: $ocms.url('rem/conf'), data: { id: remid }, success: () => {
-                            ct.trigger('modal_close');
-                            window.open($ocms.url('rem/idoc') + '?id=' + remid, '_blank');  /* open pdf in new tab */
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('rem/del'), data: {
-                                id: remid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }
-    });
 };
 $inv.sis = (id) => {
     if (confirm($ict.sisc)) {

Fuchs/js/intranet/modules/fis.inv_shared.scss

@@ -399,6 +399,33 @@
 	}
 }
 
+/* Backend-authoritative draft editing (ADR 0006): server-side plausibility findings
+   rendered above the editor, and the change-history dialog table. */
+.edit_frm .invoice_layout .dvalidation {
+	margin: 0 0 1rem 0;
+
+	&.hidden { display: none; }
+
+	.dvmsg {
+		padding: 0.4rem 0.7rem;
+		margin: 0.25rem 0;
+		border-radius: 0.2rem;
+		font-size: 0.9rem;
+		border-left: 4px solid #999;
+		background: #f5f5f5;
+
+		&.error   { border-left-color: #c0392b; background: #fdecea; color: #922; }
+		&.warning { border-left-color: #e0a800; background: #fff8e1; color: #7a5c00; }
+		&.info    { border-left-color: #3498db; background: #eaf4fb; color: #1c5a82; }
+	}
+}
+
+.dhist {
+	.invtbl { width: 100%; }
+	td, th { padding: 0.3rem 0.6rem; text-align: left; vertical-align: top; }
+	tbody tr:nth-child(even) { background: #fafafa; }
+}
+
 .modal-body .lstfrm {
 	display: block;
 	position: relative;

Fuchs/js/intranet/oci_sortable.js

@@ -63,7 +63,8 @@ if (!Element.prototype.closest) {
             this._dragging = false;
             this._dragHandleClass = this._options.dragHandleClass || '';
             this._parentident = this._options.parentident || '';
-            this._swapdone = typeof this._options.swapdone === "function" ? this._options._swapdone : null;
+            this._swapdone = typeof this._options.swapdone === "function" ? this._options.swapdone : null;
+            this._onend = typeof this._options.onend === "function" ? this._options.onend : null;
 
             this._container.setAttribute("data-is-sortable", 1);
             this._container.classList.add("sortable");
@@ -213,10 +214,17 @@ if (!Element.prototype.closest) {
             }
         },
 
-        // on item release/drop 
+        // on item release/drop
         _onRelease: function (e) {
+            // Was THIS list mid-drag? (mouseup fires on every instance's window listener.)
+            var wasDragging = this._dragging === true && this._clickItem !== null;
             this._dragging = false;
             this._trashDragItem();
+            // Fire a single "drag finished" callback so callers can commit the new order once,
+            // reliably, on drop — rather than relying on the per-hover _swapdone during the drag.
+            if (wasDragging && typeof this._onend === 'function') {
+                this._onend();
+            }
         },
 
         // on item drag/move

Fuchs/wwwroot/web/fis.inv.css

@@ -405,6 +405,50 @@ table.if td.num {
   animation: fis_spin 0.8s linear infinite;
 }
 
+/* Backend-authoritative draft editing (ADR 0006): server-side plausibility findings
+   rendered above the editor, and the change-history dialog table. */
+.edit_frm .invoice_layout .dvalidation {
+  margin: 0 0 1rem 0;
+}
+.edit_frm .invoice_layout .dvalidation.hidden {
+  display: none;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg {
+  padding: 0.4rem 0.7rem;
+  margin: 0.25rem 0;
+  border-radius: 0.2rem;
+  font-size: 0.9rem;
+  border-left: 4px solid #999;
+  background: #f5f5f5;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.error {
+  border-left-color: #c0392b;
+  background: #fdecea;
+  color: #922;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.warning {
+  border-left-color: #e0a800;
+  background: #fff8e1;
+  color: #7a5c00;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.info {
+  border-left-color: #3498db;
+  background: #eaf4fb;
+  color: #1c5a82;
+}
+
+.dhist .invtbl {
+  width: 100%;
+}
+.dhist td, .dhist th {
+  padding: 0.3rem 0.6rem;
+  text-align: left;
+  vertical-align: top;
+}
+.dhist tbody tr:nth-child(even) {
+  background: #fafafa;
+}
+
 .modal-body .lstfrm {
   display: block;
   position: relative;

Fuchs/wwwroot/web/fis.inv.de.js

@@ -646,11 +646,375 @@ $inv.eM = (r, re, opt) => {
     if ((opt || '').split(',').includes('setm') === true) {
         m.push({ lbl: $ict.setm, fnc: $inv.ssetmode });
     }
+    if ((opt || '').split(',').includes('iss') === true) {  /* backend-authoritative draft (ADR 0006) */
+        m.push({ lbl: 'Änderungshistorie', fnc: () => $inv.d.history() });
+        m.push({ lbl: 'Änderungen verwerfen', fnc: () => $inv.d.discard() });
+    }
     if (booln(r, false) === true) {
         m.push({ lbl: $ict.rel, fnc: $inv.rReload });
     }
     return $('#topbar').ocmsmenu(m);  /* empty Array => empty menu */
 };
+/* ── Backend-authoritative draft editing controller (ADR 0006/0007) ───────────
+   The server holds the truth for an invoice draft in an in-memory session; this
+   object seeds it, sends single edits as deltas, and renders the totals footer +
+   validation from the authoritative server state. It is invoice-only: reminders
+   never obtain a token (invSumUpdate, the seed trigger, is only bound for invoices),
+   so they keep the legacy stateless flow untouched. */
+$inv.d = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.d.tbl().data('dtoken') || ''; },
+    /* Hash each assembled block so only genuinely-changed blocks are sent as deltas. */
+    hashes: function () {
+        let bai = $inv.d.tbl().data('bai') || [], h = {};
+        $.each(bai, (i, b) => { h[(b.Id || '').toString()] = JSON.stringify(b); });
+        return h;
+    },
+    /* Seed the authoritative server session from the assembled editor payload. Called
+       once from invSumUpdate on open; thereafter the backend is the source of truth. */
+    seed: function (payload) {
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.d.tbl().data('dtoken', r.token).data('dver', r.version).data('dhashes', $inv.d.hashes()).data('dorder', $inv.d.order());
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.d.refresh(),
+                    onExpiring: (s) => $inv.d.warnExpiry(s),
+                    onClosed: (reason) => $inv.d.closed(reason)
+                });
+                $inv.d.refresh();
+            }, error: () => { l.rC('freeze'); }, complete: () => { $inv.d.tbl().removeData('dseeding'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the totals footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dstate'), data: { token: t }, success: (state) => {
+                $inv.d.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } },
+            complete: () => { $inv.d.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.d.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('dver', state.version).data('serverSums', state.sums);
+        $inv.d.footer(tbl, state.sums || {}, state.admin || {});
+        $inv.d.validation(state.validation || []);
+        $inv.d.applyPositions(tbl, state.req || []);
+    },
+    /* Push the server's authoritative position numbers back onto the rendered rows so the online
+       editor and the PDF preview always agree (the server numbers priced lines continuously; the
+       browser must not keep its own numbering). Only the position cell is touched — no re-render. */
+    applyPositions: function (tbl, req) {
+        (req || []).forEach((b) => (b && b.itm || []).forEach((co) => {
+            if (!co || (co.id || '') === '') { return; }
+            let cell = tbl.find('#itm' + co.id + ' td.keep').first();
+            if (cell.length) { cell.text(co.p != null ? co.p : ''); }
+        }));
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $inv.d.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.d.refresh(); },
+            error: (xhr) => { $inv.d.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } }
+        });
+    },
+    /* The current section id sequence (used to detect a reorder that changes no block content). */
+    order: function () { return (($inv.d.tbl().data('bai')) || []).map((b) => (b.Id || '').toString()); },
+    /* Diff the freshly-rebuilt blocks against the last-synced state and send only the
+       changed/removed blocks as granular block.replace / block.remove deltas. A pure section
+       reorder (same blocks, new sequence) changes no block hash, so it is sent separately as a
+       block.order delta; the server reorders the cache, renumbers positions and pushes them back. */
+    syncChanged: function (tbl) {
+        if (($inv.d.token()) === '') { return; }
+        let bai = tbl.data('bai') || [], prev = tbl.data('dhashes') || {}, next = {}, changed = [], removed = [];
+        $.each(bai, (i, b) => { let id = (b.Id || '').toString(), h = JSON.stringify(b); next[id] = h; if (prev[id] !== h) { changed.push(b); } });
+        $.each(prev, (id) => { if (next[id] === undefined) { removed.push(id); } });
+        let order = $inv.d.order(), prevOrder = tbl.data('dorder') || [];
+        tbl.data('dhashes', next).data('dorder', order);
+        changed.forEach((b) => $inv.d.sync({ Target: 'block.replace', Ref: (b.Id || '').toString(), Value: b }));
+        removed.forEach((id) => $inv.d.sync({ Target: 'block.remove', Ref: id }));
+        let sameSet = prevOrder.length === order.length && prevOrder.slice().sort().join(',') === order.slice().sort().join(',');
+        if (sameSet && prevOrder.join(',') !== order.join(',')) { $inv.d.sync({ Target: 'block.order', Value: order }); }
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.d.token() === '') { return; }
+        let map = { invoicetitle: 'title', invoiceaddress: 'address', invoiceemail: 'email', loc: 'provisionlocation', provisionlocation: 'provisionlocation', provisionperiod: 'provisionperiod' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.d.sync({ Target: target, Value: val });
+    },
+    /* Render the totals footer from the server sums (port of invSumUpdate's footer half). */
+    footer: function (tbl, sums, admin) {
+        let ft = tbl.children('tfoot').empty(); tbl.nextAll('.fnote').remove();
+        let p13b = bool(admin.p13b, false);
+        let rwcy = (lbl, val, cls) => $$.tdc('currency', $$.tr(ft, { class: cls || 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 4 }).text(lbl)]), fnum(val, $rct.cst));
+        let fn = (t) => $$.dc('fnote').insertAfter(tbl).rwText(t);
+        rwcy('Netto', sums.total_net || 0);
+        if (p13b === false) { $.each(sums.vat || {}, (rate, amt) => rwcy($rct.vat + ' ' + rate + '%', amt, 'tvat')); }
+        rwcy('Summe', sums.total_gross || 0);
+        let itype = (admin.type || '');
+        if (itype === 'i') { fn($rct.note2); fn($rct.note4); }
+        else if (itype === 'c') { fn($rct.note2); }
+        else {
+            fn(string($rct.note3, [fnum(((sums.service_net || 0) + (sums.service_vat || 0)) * (admin.tax_servicerefund || 0), $rct.cst)])).aC('ntax');
+            fn($rct.note2);
+            fn(string($rct.note1, [fnum((sums.service_net || 0) + (sums.service_vat || 0), $rct.cst), fnum(sums.service_net || 0, $rct.cst), fnum(sums.service_vat || 0, $rct.cst)]));
+        }
+        if (p13b === true) { fn($rct.note13b); }
+    },
+    validation: function (msgs) {
+        let frm = $('div.invoice_layout'); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise, cancel = discard. */
+    preview: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout();
+        let email = ($inv.d.tbl().data('new') || {}).invoiceemail || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), total = response.total;
+                if (total > 10) { $$.dc('note warn', c).text($ict.tpe); }
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                for (let ic = (response.img || []).length + 1; ic <= total; ic++) { $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna)); }
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('inv/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('req/sconf'), data: { id: sv.invid }, success: (cresp) => {
+                                        ct.trigger('modal_close');
+                                        if (cresp.hasFile === true) { window.open($ocms.url('req/idoc') + '?id=' + sv.invid, '_blank'); }
+                                        $inv.d.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.d.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dsave'), data: { token: t }, success: (r) => { $inv.d.tbl().data('invid', r.invid); },
+            error: () => { alert($ict.eis); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    discard: function () {
+        let invid = $inv.d.tbl().data('invid') || '';
+        if (invid === '') { alert('Es wurde noch kein Zwischenstand gespeichert, der wiederhergestellt werden könnte.'); return; }
+        if (confirm('Alle Änderungen verwerfen und den zuletzt gespeicherten Stand neu laden?') === false) { return; }
+        $inv.d.close();
+        $inv.cntInv({ id: invid });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Rechnungsentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.d.token();
+        $inv.d.tbl().removeData('dtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Rechnungsentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Rechnungsentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.d.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('inv/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.d.tbl().removeData('dtoken');
+    }
+};
+/* ── Backend-authoritative reminder draft editing (ADR 0006/0007) ─────────────
+   The reminder mirror of $inv.d: the server holds the truth for a reminder draft in
+   an in-memory session; this object seeds it (rem/dopen), sends single edits as deltas
+   (rem/dpatch), and renders the open-amount footer + validation from the authoritative
+   server state (rem/dstate). Preview renders straight from the cache (rem/dpreview);
+   confirm flushes (rem/dsave) then finalises + emails (rem/conf). It coexists with $inv.d
+   on the same DOM: each keys off its own token (rdtoken vs dtoken), so the shared inline
+   editor safely no-ops for the mode that is not active. */
+$inv.rd = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.rd.tbl().data('rdtoken') || ''; },
+    /* Seed the authoritative server session from the assembled reminder editor payload. */
+    seed: function (payload) {
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.rd.tbl().data('rdtoken', r.token).data('rdver', r.version);
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.rd.refresh(),
+                    onExpiring: (s) => $inv.rd.warnExpiry(s),
+                    onClosed: (reason) => $inv.rd.closed(reason)
+                });
+                $inv.rd.refresh();
+            }, error: () => { l.rC('freeze'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the open-amount footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dstate'), data: { token: t }, success: (state) => {
+                $inv.rd.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } },
+            complete: () => { $inv.rd.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.rd.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('rdver', state.version).data('serverSums', state.sums).data('remid', state.remid || '');
+        $inv.rd.footer(tbl, state.sums || {});
+        $inv.rd.validation(state.validation || []);
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $inv.rd.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.rd.refresh(); },
+            error: (xhr) => { $inv.rd.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } }
+        });
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.rd.token() === '') { return; }
+        let map = { subject: 'subject', invoiceaddress: 'address', invoiceemail: 'email', text: 'text' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.rd.sync({ Target: target, Value: val });
+    },
+    /* Amount / amount-paid come from the item-row dialog; send both as their own deltas. */
+    syncAmount: function (amount, amount_payed) {
+        if ($inv.rd.token() === '') { return; }
+        $inv.rd.sync({ Target: 'amount', Value: (amount != null ? amount : 0).toString() });
+        $inv.rd.sync({ Target: 'amount_payed', Value: (amount_payed != null ? amount_payed : 0).toString() });
+    },
+    /* Render the open-amount footer from the server sums. */
+    footer: function (tbl, sums) {
+        let ft = tbl.children('tfoot').empty();
+        let tr = $$.tr(ft, { class: 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 3 }).text('Offener Betrag')]);
+        $$.tdc('currency', tr, fnum(sums.amount_open || 0, $rct.cst));
+    },
+    validation: function (msgs) {
+        let frm = $inv.rd.layout(); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise + email, cancel = discard. */
+    preview: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout();
+        let email = (($inv.rd.tbl().data('new') || {}).invoiceemail) || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88);
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('rem/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('rem/conf'), data: { id: sv.remid }, success: () => {
+                                        ct.trigger('modal_close');
+                                        window.open($ocms.url('rem/idoc') + '?id=' + sv.remid, '_blank');
+                                        $inv.rd.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($t.f1); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.rd.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($t.f1); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dsave'), data: { token: t }, success: (r) => { $inv.rd.tbl().data('remid', r.remid); },
+            error: () => { alert($t.f1); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Mahnentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.rd.token();
+        $inv.rd.tbl().removeData('rdtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Mahnentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Mahnentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.rd.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('rem/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.rd.tbl().removeData('rdtoken');
+    }
+};
 $inv.cInv2 = function (data) {
     let fr = $$.dc('rfrm').ldng(1);
     let o = $ocms.dlg(fr, { width: 1000 });
@@ -1028,9 +1392,12 @@ $inv.cSt = function (data) {
 };
 $inv.eHtml = function (ev) {
     let t = $(this), frmct = ev.data instanceof jQuery ? ev.data : ev.data.t;
-    /* invoiceemail must stay plain text — using the TinyMCE/html editor here used to wrap the
+    /* Single-line fields must stay plain text — the TinyMCE/html editor wraps the value in <p>
-       address in <p> tags, which then got posted and persisted verbatim into SendToEmail. */
+       tags, which used to get posted and persisted verbatim (e.g. <p>18.06.2026</p> in the
-    let isPlainText = ev.data.nme === 'invoiceemail';
+       Leistungsdatum). The backend sanitises HTML too (single source of truth, ADR 0006), but
+       keeping these plain here avoids the UI briefly holding the wrapped value. Multi-line fields
+       (invoiceaddress, loc) stay HTML-capable and are normalised to newlines server-side. */
+    let isPlainText = ['invoiceemail', 'provisionperiod', 'invoicetitle'].includes(ev.data.nme);
     let flds = isPlainText
         ? [{ name: 'txt', label: 'Text', type: 'text', value: frmct.text() }]
         : [{ name: 'txt', label: 'Text', type: 'html', value: frmct.html(), tinymce: true, attr: { style: 'height: 300px' } }];
@@ -1046,6 +1413,11 @@ $inv.eHtml = function (ev) {
             if (typeof change === 'function') {
                 change(response.txt);
             }
+            /* backend-authoritative: mirror the inline recipient-field edit to the server session.
+               Invoice and reminder editors share this DOM; each syncField no-ops unless its own
+               draft token is present, so only the active mode's session receives the delta. */
+            $inv.d.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
+            $inv.rd.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
         },
         tinymce: { valid_elements: 'br', hidemenu: true, hidetoolbar: true }
     }
@@ -1131,7 +1503,11 @@ $inv.eRw = function(row, dta, flds) {
         }, typedvalues: true
     });
 };
-$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', swapdone: (p1, p2, i1, i2) => { $inv.t_fds_inv(); } }) }
+/* Reorder items via drag. The DOM swap happens inside the Sortable during the drag; we commit
+   the new order once, reliably, on drop (onend) — that recomputes positions/totals and pushes the
+   changed block(s) to the backend session (t_fds_inv -> syncChanged). Committing on drop (rather
+   than on every mid-drag hover-swap) avoids rebuilding the row that is currently being dragged. */
+$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', onend: () => { $inv.t_fds_inv(); } }) }
 $inv.rrw = function () {
     let rw = $(this), dta = rw.data(), co = {}, ph = rw.is('.placeholder'), hn = rw.is('.hidenote');
     let oHtml = (e) => $$.d().append(e).html();
@@ -1260,6 +1636,13 @@ $inv.invSumUpdate = function () {
     }
     tbl.data('sms', sms);
     tbl.data('bai', ba);
+    /* Backend-authoritative seeding (ADR 0006): on the first calculation of an invoice
+       draft (invSumUpdate is only bound for invoices, never reminders), hand the assembled
+       model to the server session and switch to server-driven totals from then on. */
+    if ((tbl.data('dtoken') || '') === '' && bool(tbl.data('dseeding'), false) === false && ((tbl.data('admin') || {}).type != null)) {
+        tbl.data('dseeding', true);
+        $inv.d.seed($.extend($inv.invcPayload(tbl.data()), { invid: tbl.data('invid') || '' }));
+    }
 };
 $inv.worknotes = function (rx) {
     let wn = '';
@@ -1347,7 +1730,13 @@ $inv.rendersrq = function () {
         $$.tdc('currency isumval', istr);
     }
 };
-$inv.t_fds_inv = () => { $('div.invoice_layout table.invi').trigger('fds.inv'); };
+$inv.t_fds_inv = () => {
+    let tbl = $('div.invoice_layout table.invi');
+    tbl.trigger('fds.inv');
+    /* After any local item mutation, push the changed block(s) to the authoritative
+       server session as granular deltas (invoice drafts only — reminders have no token). */
+    if ((tbl.data('dtoken') || '') !== '') { $inv.d.syncChanged(tbl); }
+};
 $inv.sedit = () => {
     $inv.sprev(true);
 };
@@ -1402,6 +1791,7 @@ $inv.sp13b = () => {
     } else {
     }
     tbl.trigger('fds.inv');
+    $inv.d.sync({ Target: 'p13b', Value: d.admin.p13b });
 };
 /* Maps an item row's data to the backend item contract consumed by InvoiceSetPricing
    / FuchsPdf.ApplyInvoice: { id, type, title (plain), desc (html), qty, price_net,
@@ -1456,6 +1846,7 @@ $inv.setSetmode = (mode) => {
     let opts = (d.inv.InvoiceOptions || '').split(',').filter(x => x !== '' && x.indexOf('setmode:') !== 0);
     if (mode && mode !== 'setprice') { opts.push('setmode:' + mode); }
     d.inv.InvoiceOptions = opts.join(',');
+    $inv.d.sync({ Target: 'setmode', Value: mode });
 };
 $inv.sctp = () => {
     let flds = $invcol.ctp;
@@ -1472,6 +1863,7 @@ $inv.sctp = () => {
             cvo.contactEmail = response.email;
             d.new.CustomValues = JSON.stringify(cvo);  //Assign it to new Values so that this is submitted also
             l.find('.ctpfrm').text(ne(response.name, response.email));
+            $inv.d.sync({ Target: 'contact', Value: { name: response.name, email: response.email } });
 
         }, typedvalues: true
     });
@@ -1496,82 +1888,12 @@ $inv.invcPayload = function (d) {
     adm.customerid = (adm.customerid != null ? adm.customerid : adm.CustomerId);
     return { admin: adm, req: d.bai, sms: d.sms, new: nw };
 };
-$inv.ssave = () => {
+/* Zwischenspeichern and preview now run against the backend-authoritative session
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
+   (ADR 0006): no full-invoice re-upload — the cached draft is flushed / rendered by
-    $inv.t_fds_inv();
+   token. See $inv.d.save / $inv.d.preview. The finalise + email path (req/sconf) is
-    l.aC('freeze');
+   unchanged and is invoked from the preview modal's confirm handler. */
-    $ocms.postXT({
+$inv.ssave = () => { $inv.d.save(); };
-        url: $ocms.url('req/save'), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid || '' }, success: (response) => {
+$inv.sprev = (change) => { $inv.d.preview(); };
-            $inv.cntInv({ id: response.id });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
-$inv.sprev = (change) => {
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
-    change = bool(change, false);
-    $inv.t_fds_inv();
-    l.aC('freeze');
-    //console.debug({ admin: d.admin, req: d.bai, sms: d.sms, new: d.new });
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc),false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('req/' + (change === true ?'sedit':'sprep')), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid ||'' }, success: (response) => {
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), invid = response.id, invtp = response.total;
-            if (invtp > 10) {
-                $$.dc('note warn', c).text($ict.tpe);
-            }
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            for (let ic = (response.img || []).length + 1; ic <= invtp; ic++) {
-                $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna));
-            }
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI, confirm: function (e) {
-                    let ct = $(this);
-                    l.aC('freeze');  /* spinner while the invoice is finalized/emailed on the backend */
-                    $ocms.postXT({
-                        url: $ocms.url('req/sconf'), data: { id: invid }, success: (cresp) => {
-                            ct.trigger('modal_close');
-                            if (cresp.hasFile === true) {
-                                window.open($ocms.url('req/idoc') + '?id=' + invid, '_blank');  /* open pdf in new tab, only if a file was actually created */
-                            }
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }, complete: () => {
-                            l.rC('freeze');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('req/sdel'), data: {
-                                id: invid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
 $inv.rReload = () => {
     try {
         let s = $('#listframe ul.rql:first').data();
@@ -1750,6 +2072,8 @@ $inv.eRowR = function (ev) {
             $.extend(tdta.rm, res);
             tbl.data(tdta);
             $inv.rRemRw.call(row, tdta);
+            /* backend-authoritative: mirror the edited amount / amount-paid to the server session */
+            $inv.rd.syncAmount(tdta.rm.amount, tdta.rm.amount_payed);
         }, typedvalues: true
     });
 };
@@ -1790,57 +2114,26 @@ $inv.ccRem_s2 = function (id, sets) {  //reminder creation
             rif.tbl.children('tbody').each($inv.bdysort);
             rif.tbl.trigger('fds.inv');  /* trigger calculations */
 
+            /* Seed the authoritative server session (ADR 0006). Amounts join the recipient
+               fields in the 'new' block; the reference invoice data goes into 'rem'. From here
+               the backend owns the open-amount computation and validation; inline edits and the
+               item-row dialog post single deltas (see $inv.rd). */
+            let nw = rif.tbl.data('new');
+            nw.amount = rem.amount; nw.amount_payed = rem.amount_payed;
+            $inv.rd.seed({
+                rem: { invid: rem.invid, type: rem.type, invoiceid: rem.invoiceid, invoicedate: rem.invoicedate },
+                new: nw
+            });
         }, complete: () => {
             //o.c.trigger('modal_close');
         }
     });
 };
 $inv.rprev = () => {
-    var l = $('div.invoice_layout'), tbl = l.find('table.invi'), d = tbl.data();
+    /* Preview + finalise now run through the backend-authoritative session ($inv.rd):
-    $.extend(d.new, tbl.find('tbody > tr:first').data());
+       the PDF renders straight from the server cache (no rem/prep DB write), and confirm
-    l.aC('freeze');
+       flushes (rem/dsave) then finalises + emails (rem/conf). */
-    //console.debug({ rem: d.rm, new: d.new });
+    $inv.rd.preview();
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('rem/prep'), data: { remc: JSON.stringify({ rem: d.rm, new: d.new }), id: d.invid || '' }, success: (response) => {
-            l.rC('freeze');
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), remid = response.id;
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd, confirm: function (e) {
-                    let ct = $(this);
-                    $ocms.postXT({
-                        url: $ocms.url('rem/conf'), data: { id: remid }, success: () => {
-                            ct.trigger('modal_close');
-                            window.open($ocms.url('rem/idoc') + '?id=' + remid, '_blank');  /* open pdf in new tab */
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('rem/del'), data: {
-                                id: remid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }
-    });
 };
 $inv.sis = (id) => {
     if (confirm($ict.sisc)) {

Fuchs/wwwroot/web/fis.js

@@ -2533,7 +2533,8 @@ if (!Element.prototype.closest) {
             this._dragging = false;
             this._dragHandleClass = this._options.dragHandleClass || '';
             this._parentident = this._options.parentident || '';
-            this._swapdone = typeof this._options.swapdone === "function" ? this._options._swapdone : null;
+            this._swapdone = typeof this._options.swapdone === "function" ? this._options.swapdone : null;
+            this._onend = typeof this._options.onend === "function" ? this._options.onend : null;
 
             this._container.setAttribute("data-is-sortable", 1);
             this._container.classList.add("sortable");
@@ -2683,10 +2684,17 @@ if (!Element.prototype.closest) {
             }
         },
 
-        // on item release/drop 
+        // on item release/drop
         _onRelease: function (e) {
+            // Was THIS list mid-drag? (mouseup fires on every instance's window listener.)
+            var wasDragging = this._dragging === true && this._clickItem !== null;
             this._dragging = false;
             this._trashDragItem();
+            // Fire a single "drag finished" callback so callers can commit the new order once,
+            // reliably, on drop — rather than relying on the per-hover _swapdone during the drag.
+            if (wasDragging && typeof this._onend === 'function') {
+                this._onend();
+            }
         },
 
         // on item drag/move
@@ -3129,6 +3137,68 @@ $fis.notifications = {
     }
 };
 
+/* Live draft-editing client (ADR 0006/0007). Separate SignalR connection to the
+   dedicated /draftpreview hub; the server signals the *one* browser editing a draft
+   (group = session token) to re-fetch (draftReady), warns before idle expiry
+   (draftExpiring), and tells it to close on eviction (draftClosed). The editor
+   (fis.inv_shared.js) registers the open draft via $fis.draft.bind(token, {...}). */
+$fis.draft = {
+    connection: null,
+    active: null,   /* { token, onReady(version), onExpiring(secondsLeft), onClosed(reason) } */
+    init: function () {
+        if (typeof signalR === 'undefined' || this.connection !== null || !$ocms.auth.useraccount_id) {
+            return;
+        }
+        this.connection = new signalR.HubConnectionBuilder()
+            .withUrl('/draftpreview')
+            .withAutomaticReconnect()
+            .build();
+        this.connection.on('draftReady',    (p) => this._dispatch('onReady',    p, (p) => p.version));
+        this.connection.on('draftExpiring', (p) => this._dispatch('onExpiring', p, (p) => p.secondsLeft));
+        this.connection.on('draftClosed',   (p) => this._dispatch('onClosed',   p, (p) => p.reason));
+        /* Re-join the active draft's group after a (re)connect — group membership is
+           per-connection and is lost when the socket drops. */
+        this.connection.onreconnected(() => { if (this.active) { this._invoke('JoinDraft', this.active.token); } });
+        this.connection.onclose(() => {
+            console.warn('Draft connection closed; retrying in 5s.');
+            this.connection = null;
+            setTimeout(() => { this.init(); if (this.active) { this.bind(this.active.token, this.active); } }, 5000);
+        });
+        this.start();
+    },
+    start: function () {
+        this.connection.start()
+            .then(() => { if (this.active) { this._invoke('JoinDraft', this.active.token); } })
+            .catch((err) => {
+                console.warn('Draft connection failed to start; retrying in 5s.', err);
+                this.connection = null;
+                setTimeout(() => this.init(), 5000);
+            });
+    },
+    /* Registers the currently open draft and joins its signal group. handlers:
+       { onReady, onExpiring, onClosed }. */
+    bind: function (token, handlers) {
+        if (!token) { return; }
+        this.active = $.extend({ token: token }, handlers || {});
+        if (this.connection === null) { this.init(); }
+        this._invoke('JoinDraft', token);
+    },
+    /* Unregisters + leaves the group (editor closed). */
+    release: function (token) {
+        if (this.active && (!token || this.active.token === token)) { this.active = null; }
+        this._invoke('LeaveDraft', token);
+    },
+    _invoke: function (method, token) {
+        if (!token || !this.connection || this.connection.state !== 'Connected') { return; }
+        this.connection.invoke(method, token).catch((err) => console.warn('Draft ' + method + ' failed', err));
+    },
+    _dispatch: function (handler, payload, argOf) {
+        payload = payload || {};
+        if (!this.active || this.active.token !== payload.token) { return; }
+        if (typeof this.active[handler] === 'function') { this.active[handler](argOf(payload)); }
+    }
+};
+
 (function () {
     Array.prototype.push.apply($ocms.ocmsmenu,[
         { lbl: $t.m_inv, id: 'm_inv', fnc: 'init:inv', ico: 'glyphicon glyphicon-list-alt'}
@@ -3143,5 +3213,6 @@ $fis.notifications = {
 })();
 $(document).ready(function () {
     $fis.notifications.init();
+    $fis.draft.init();
     $fis.ov();
 });

Fuchs/wwwroot/web/fis.req.css

@@ -542,6 +542,50 @@ table.if th.keep, table.if td.keep {
   animation: fis_spin 0.8s linear infinite;
 }
 
+/* Backend-authoritative draft editing (ADR 0006): server-side plausibility findings
+   rendered above the editor, and the change-history dialog table. */
+.edit_frm .invoice_layout .dvalidation {
+  margin: 0 0 1rem 0;
+}
+.edit_frm .invoice_layout .dvalidation.hidden {
+  display: none;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg {
+  padding: 0.4rem 0.7rem;
+  margin: 0.25rem 0;
+  border-radius: 0.2rem;
+  font-size: 0.9rem;
+  border-left: 4px solid #999;
+  background: #f5f5f5;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.error {
+  border-left-color: #c0392b;
+  background: #fdecea;
+  color: #922;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.warning {
+  border-left-color: #e0a800;
+  background: #fff8e1;
+  color: #7a5c00;
+}
+.edit_frm .invoice_layout .dvalidation .dvmsg.info {
+  border-left-color: #3498db;
+  background: #eaf4fb;
+  color: #1c5a82;
+}
+
+.dhist .invtbl {
+  width: 100%;
+}
+.dhist td, .dhist th {
+  padding: 0.3rem 0.6rem;
+  text-align: left;
+  vertical-align: top;
+}
+.dhist tbody tr:nth-child(even) {
+  background: #fafafa;
+}
+
 .modal-body .lstfrm {
   display: block;
   position: relative;

Fuchs/wwwroot/web/fis.req.de.js

@@ -627,11 +627,375 @@ $inv.eM = (r, re, opt) => {
     if ((opt || '').split(',').includes('setm') === true) {
         m.push({ lbl: $ict.setm, fnc: $inv.ssetmode });
     }
+    if ((opt || '').split(',').includes('iss') === true) {  /* backend-authoritative draft (ADR 0006) */
+        m.push({ lbl: 'Änderungshistorie', fnc: () => $inv.d.history() });
+        m.push({ lbl: 'Änderungen verwerfen', fnc: () => $inv.d.discard() });
+    }
     if (booln(r, false) === true) {
         m.push({ lbl: $ict.rel, fnc: $inv.rReload });
     }
     return $('#topbar').ocmsmenu(m);  /* empty Array => empty menu */
 };
+/* ── Backend-authoritative draft editing controller (ADR 0006/0007) ───────────
+   The server holds the truth for an invoice draft in an in-memory session; this
+   object seeds it, sends single edits as deltas, and renders the totals footer +
+   validation from the authoritative server state. It is invoice-only: reminders
+   never obtain a token (invSumUpdate, the seed trigger, is only bound for invoices),
+   so they keep the legacy stateless flow untouched. */
+$inv.d = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.d.tbl().data('dtoken') || ''; },
+    /* Hash each assembled block so only genuinely-changed blocks are sent as deltas. */
+    hashes: function () {
+        let bai = $inv.d.tbl().data('bai') || [], h = {};
+        $.each(bai, (i, b) => { h[(b.Id || '').toString()] = JSON.stringify(b); });
+        return h;
+    },
+    /* Seed the authoritative server session from the assembled editor payload. Called
+       once from invSumUpdate on open; thereafter the backend is the source of truth. */
+    seed: function (payload) {
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.d.tbl().data('dtoken', r.token).data('dver', r.version).data('dhashes', $inv.d.hashes()).data('dorder', $inv.d.order());
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.d.refresh(),
+                    onExpiring: (s) => $inv.d.warnExpiry(s),
+                    onClosed: (reason) => $inv.d.closed(reason)
+                });
+                $inv.d.refresh();
+            }, error: () => { l.rC('freeze'); }, complete: () => { $inv.d.tbl().removeData('dseeding'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the totals footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dstate'), data: { token: t }, success: (state) => {
+                $inv.d.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } },
+            complete: () => { $inv.d.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.d.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('dver', state.version).data('serverSums', state.sums);
+        $inv.d.footer(tbl, state.sums || {}, state.admin || {});
+        $inv.d.validation(state.validation || []);
+        $inv.d.applyPositions(tbl, state.req || []);
+    },
+    /* Push the server's authoritative position numbers back onto the rendered rows so the online
+       editor and the PDF preview always agree (the server numbers priced lines continuously; the
+       browser must not keep its own numbering). Only the position cell is touched — no re-render. */
+    applyPositions: function (tbl, req) {
+        (req || []).forEach((b) => (b && b.itm || []).forEach((co) => {
+            if (!co || (co.id || '') === '') { return; }
+            let cell = tbl.find('#itm' + co.id + ' td.keep').first();
+            if (cell.length) { cell.text(co.p != null ? co.p : ''); }
+        }));
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $inv.d.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.d.refresh(); },
+            error: (xhr) => { $inv.d.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.d.closed('expired'); } }
+        });
+    },
+    /* The current section id sequence (used to detect a reorder that changes no block content). */
+    order: function () { return (($inv.d.tbl().data('bai')) || []).map((b) => (b.Id || '').toString()); },
+    /* Diff the freshly-rebuilt blocks against the last-synced state and send only the
+       changed/removed blocks as granular block.replace / block.remove deltas. A pure section
+       reorder (same blocks, new sequence) changes no block hash, so it is sent separately as a
+       block.order delta; the server reorders the cache, renumbers positions and pushes them back. */
+    syncChanged: function (tbl) {
+        if (($inv.d.token()) === '') { return; }
+        let bai = tbl.data('bai') || [], prev = tbl.data('dhashes') || {}, next = {}, changed = [], removed = [];
+        $.each(bai, (i, b) => { let id = (b.Id || '').toString(), h = JSON.stringify(b); next[id] = h; if (prev[id] !== h) { changed.push(b); } });
+        $.each(prev, (id) => { if (next[id] === undefined) { removed.push(id); } });
+        let order = $inv.d.order(), prevOrder = tbl.data('dorder') || [];
+        tbl.data('dhashes', next).data('dorder', order);
+        changed.forEach((b) => $inv.d.sync({ Target: 'block.replace', Ref: (b.Id || '').toString(), Value: b }));
+        removed.forEach((id) => $inv.d.sync({ Target: 'block.remove', Ref: id }));
+        let sameSet = prevOrder.length === order.length && prevOrder.slice().sort().join(',') === order.slice().sort().join(',');
+        if (sameSet && prevOrder.join(',') !== order.join(',')) { $inv.d.sync({ Target: 'block.order', Value: order }); }
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.d.token() === '') { return; }
+        let map = { invoicetitle: 'title', invoiceaddress: 'address', invoiceemail: 'email', loc: 'provisionlocation', provisionlocation: 'provisionlocation', provisionperiod: 'provisionperiod' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.d.sync({ Target: target, Value: val });
+    },
+    /* Render the totals footer from the server sums (port of invSumUpdate's footer half). */
+    footer: function (tbl, sums, admin) {
+        let ft = tbl.children('tfoot').empty(); tbl.nextAll('.fnote').remove();
+        let p13b = bool(admin.p13b, false);
+        let rwcy = (lbl, val, cls) => $$.tdc('currency', $$.tr(ft, { class: cls || 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 4 }).text(lbl)]), fnum(val, $rct.cst));
+        let fn = (t) => $$.dc('fnote').insertAfter(tbl).rwText(t);
+        rwcy('Netto', sums.total_net || 0);
+        if (p13b === false) { $.each(sums.vat || {}, (rate, amt) => rwcy($rct.vat + ' ' + rate + '%', amt, 'tvat')); }
+        rwcy('Summe', sums.total_gross || 0);
+        let itype = (admin.type || '');
+        if (itype === 'i') { fn($rct.note2); fn($rct.note4); }
+        else if (itype === 'c') { fn($rct.note2); }
+        else {
+            fn(string($rct.note3, [fnum(((sums.service_net || 0) + (sums.service_vat || 0)) * (admin.tax_servicerefund || 0), $rct.cst)])).aC('ntax');
+            fn($rct.note2);
+            fn(string($rct.note1, [fnum((sums.service_net || 0) + (sums.service_vat || 0), $rct.cst), fnum(sums.service_net || 0, $rct.cst), fnum(sums.service_vat || 0, $rct.cst)]));
+        }
+        if (p13b === true) { fn($rct.note13b); }
+    },
+    validation: function (msgs) {
+        let frm = $('div.invoice_layout'); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise, cancel = discard. */
+    preview: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout();
+        let email = ($inv.d.tbl().data('new') || {}).invoiceemail || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), total = response.total;
+                if (total > 10) { $$.dc('note warn', c).text($ict.tpe); }
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                for (let ic = (response.img || []).length + 1; ic <= total; ic++) { $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna)); }
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('inv/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('req/sconf'), data: { id: sv.invid }, success: (cresp) => {
+                                        ct.trigger('modal_close');
+                                        if (cresp.hasFile === true) { window.open($ocms.url('req/idoc') + '?id=' + sv.invid, '_blank'); }
+                                        $inv.d.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.d.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($ict.eis); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        let l = $inv.d.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('inv/dsave'), data: { token: t }, success: (r) => { $inv.d.tbl().data('invid', r.invid); },
+            error: () => { alert($ict.eis); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.d.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('inv/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    discard: function () {
+        let invid = $inv.d.tbl().data('invid') || '';
+        if (invid === '') { alert('Es wurde noch kein Zwischenstand gespeichert, der wiederhergestellt werden könnte.'); return; }
+        if (confirm('Alle Änderungen verwerfen und den zuletzt gespeicherten Stand neu laden?') === false) { return; }
+        $inv.d.close();
+        $inv.cntInv({ id: invid });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Rechnungsentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.d.token();
+        $inv.d.tbl().removeData('dtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Rechnungsentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Rechnungsentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.d.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('inv/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.d.tbl().removeData('dtoken');
+    }
+};
+/* ── Backend-authoritative reminder draft editing (ADR 0006/0007) ─────────────
+   The reminder mirror of $inv.d: the server holds the truth for a reminder draft in
+   an in-memory session; this object seeds it (rem/dopen), sends single edits as deltas
+   (rem/dpatch), and renders the open-amount footer + validation from the authoritative
+   server state (rem/dstate). Preview renders straight from the cache (rem/dpreview);
+   confirm flushes (rem/dsave) then finalises + emails (rem/conf). It coexists with $inv.d
+   on the same DOM: each keys off its own token (rdtoken vs dtoken), so the shared inline
+   editor safely no-ops for the mode that is not active. */
+$inv.rd = {
+    tbl: () => $('div.invoice_layout table.invi'),
+    layout: () => $('div.invoice_layout'),
+    token: function () { return $inv.rd.tbl().data('rdtoken') || ''; },
+    /* Seed the authoritative server session from the assembled reminder editor payload. */
+    seed: function (payload) {
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dopen'), data: { payload: JSON.stringify(payload) }, success: (r) => {
+                $inv.rd.tbl().data('rdtoken', r.token).data('rdver', r.version);
+                $fis.draft.bind(r.token, {
+                    onReady: () => $inv.rd.refresh(),
+                    onExpiring: (s) => $inv.rd.warnExpiry(s),
+                    onClosed: (reason) => $inv.rd.closed(reason)
+                });
+                $inv.rd.refresh();
+            }, error: () => { l.rC('freeze'); }
+        });
+    },
+    /* Re-fetch the authoritative state and render the open-amount footer + validation from it. */
+    refresh: function (cb) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dstate'), data: { token: t }, success: (state) => {
+                $inv.rd.applyState(state); if (typeof cb === 'function') { cb(state); }
+            }, error: (xhr) => { if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } },
+            complete: () => { $inv.rd.layout().rC('freeze'); }
+        });
+    },
+    applyState: function (state) {
+        let tbl = $inv.rd.tbl(); if (tbl.length < 1) { return; }
+        tbl.data('rdver', state.version).data('serverSums', state.sums).data('remid', state.remid || '');
+        $inv.rd.footer(tbl, state.sums || {});
+        $inv.rd.validation(state.validation || []);
+    },
+    /* Send one change to the server; the draftReady signal and this success both refresh. */
+    sync: function (delta) {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $inv.rd.layout().aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpatch'), data: { token: t, delta: JSON.stringify(delta) },
+            success: () => { $inv.rd.refresh(); },
+            error: (xhr) => { $inv.rd.layout().rC('freeze'); if (xhr && xhr.status === 410) { $inv.rd.closed('expired'); } }
+        });
+    },
+    /* Map an inline recipient field to its delta target and send it. */
+    syncField: function (nme, val) {
+        if ($inv.rd.token() === '') { return; }
+        let map = { subject: 'subject', invoiceaddress: 'address', invoiceemail: 'email', text: 'text' };
+        let target = map[nme]; if (!target) { return; }
+        $inv.rd.sync({ Target: target, Value: val });
+    },
+    /* Amount / amount-paid come from the item-row dialog; send both as their own deltas. */
+    syncAmount: function (amount, amount_payed) {
+        if ($inv.rd.token() === '') { return; }
+        $inv.rd.sync({ Target: 'amount', Value: (amount != null ? amount : 0).toString() });
+        $inv.rd.sync({ Target: 'amount_payed', Value: (amount_payed != null ? amount_payed : 0).toString() });
+    },
+    /* Render the open-amount footer from the server sums. */
+    footer: function (tbl, sums) {
+        let ft = tbl.children('tfoot').empty();
+        let tr = $$.tr(ft, { class: 'tsum' }).append([$$.tdc('aux'), $$.td({ colspan: 3 }).text('Offener Betrag')]);
+        $$.tdc('currency', tr, fnum(sums.amount_open || 0, $rct.cst));
+    },
+    validation: function (msgs) {
+        let frm = $inv.rd.layout(); if (frm.length < 1) { return; }
+        let box = frm.children('.dvalidation');
+        if (box.length < 1) { box = $$.dc('dvalidation'); frm.prepend(box); }
+        box.empty().tC('hidden', (msgs || []).length < 1);
+        $.each(msgs || [], (i, m) => $$.dc('dvmsg', box).aC(m.severity).text(m.message));
+    },
+    /* PDF preview straight from the cache; confirm = flush + finalise + email, cancel = discard. */
+    preview: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout();
+        let email = (($inv.rd.tbl().data('new') || {}).invoiceemail) || '';
+        if ($fis.ValidateEmail(email) === false) { if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) { return; } }
+        l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dpreview'), data: { token: t }, success: (response) => {
+                l.rC('freeze');
+                let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88);
+                $.each(response.img || [], (ii, img) => { $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px')); });
+                $ocms.dlg(c, {
+                    size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd,
+                    confirm: function (e) {
+                        let ct = $(this); l.aC('freeze');
+                        $ocms.postXT({
+                            url: $ocms.url('rem/dsave'), data: { token: t }, success: (sv) => {
+                                $ocms.postXT({
+                                    url: $ocms.url('rem/conf'), data: { id: sv.remid }, success: () => {
+                                        ct.trigger('modal_close');
+                                        window.open($ocms.url('rem/idoc') + '?id=' + sv.remid, '_blank');
+                                        $inv.rd.close();
+                                        $ocms.init('req'); $inv.rReload();
+                                    }, error: () => { alert($t.f1); ct.trigger('modal_close'); }, complete: () => { l.rC('freeze'); }
+                                });
+                            }, error: () => { l.rC('freeze'); alert($t.f1); }
+                        });
+                    },
+                    cancel: function (e) { if (confirm($ict.cdI)) { $inv.rd.close(); $inv.rReload(); } }
+                });
+            }, error: () => { l.rC('freeze'); alert($t.f1); }
+        });
+    },
+    /* Zwischenspeichern: flush the cache to the DB (no re-upload); stay in the editor. */
+    save: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        let l = $inv.rd.layout(); l.aC('freeze');
+        $ocms.postXT({
+            url: $ocms.url('rem/dsave'), data: { token: t }, success: (r) => { $inv.rd.tbl().data('remid', r.remid); },
+            error: () => { alert($t.f1); }, complete: () => { l.rC('freeze'); }
+        });
+    },
+    history: function () {
+        let t = $inv.rd.token(); if (t === '') { return; }
+        $ocms.postXT({
+            url: $ocms.url('rem/dhistory'), data: { token: t }, success: (r) => {
+                let c = $$.dc('dhist');
+                if ((r.history || []).length < 1) { $$.dc('note', c).text('Noch keine Änderungen erfasst.'); }
+                else {
+                    let ts = $$.tblset({ class: 'invtbl fullwidth' }, c);
+                    $$.tr(ts.hd).append([$$.th().text('Zeit'), $$.th().text('Feld'), $$.th().text('Alt'), $$.th().text('Neu')]);
+                    $.each(r.history, (i, h) => $$.tr(ts.bdy).append([$$.tdc('keep', fdt(h.timestamp)), $$.td().text(h.target), $$.td().text(h.oldValue), $$.td().text(h.newValue)]));
+                }
+                $ocms.dlg(c, { width: 800, form: false });
+            }
+        });
+    },
+    warnExpiry: function (secondsLeft) {
+        let mins = Math.max(1, Math.round((secondsLeft || 0) / 60));
+        $fis.notifications.push({ severity: 'info', title: 'Entwurf läuft ab', message: 'Der Mahnentwurf läuft in etwa ' + mins + ' Minute(n) ab. Bitte zwischenspeichern, sonst gehen die Änderungen verloren.' });
+    },
+    closed: function (reason) {
+        let t = $inv.rd.token();
+        $inv.rd.tbl().removeData('rdtoken');
+        if (t !== '') { $fis.draft.release(t); }
+        $fis.frm_edit().remove(); $fis.lf(true);
+        $fis.notifications.push({ severity: 'error', title: 'Entwurf geschlossen', message: reason === 'expired' ? 'Der Mahnentwurf ist wegen Inaktivität abgelaufen. Nicht gespeicherte Änderungen sind verloren.' : 'Der Mahnentwurf wurde geschlossen.' });
+        try { $inv.rReload(); } catch (e) { }
+    },
+    close: function () {
+        let t = $inv.rd.token();
+        if (t !== '') { $ocms.postXT({ url: $ocms.url('rem/dclose'), data: { token: t } }); $fis.draft.release(t); }
+        $inv.rd.tbl().removeData('rdtoken');
+    }
+};
 $inv.cInv2 = function (data) {
     let fr = $$.dc('rfrm').ldng(1);
     let o = $ocms.dlg(fr, { width: 1000 });
@@ -1009,9 +1373,12 @@ $inv.cSt = function (data) {
 };
 $inv.eHtml = function (ev) {
     let t = $(this), frmct = ev.data instanceof jQuery ? ev.data : ev.data.t;
-    /* invoiceemail must stay plain text — using the TinyMCE/html editor here used to wrap the
+    /* Single-line fields must stay plain text — the TinyMCE/html editor wraps the value in <p>
-       address in <p> tags, which then got posted and persisted verbatim into SendToEmail. */
+       tags, which used to get posted and persisted verbatim (e.g. <p>18.06.2026</p> in the
-    let isPlainText = ev.data.nme === 'invoiceemail';
+       Leistungsdatum). The backend sanitises HTML too (single source of truth, ADR 0006), but
+       keeping these plain here avoids the UI briefly holding the wrapped value. Multi-line fields
+       (invoiceaddress, loc) stay HTML-capable and are normalised to newlines server-side. */
+    let isPlainText = ['invoiceemail', 'provisionperiod', 'invoicetitle'].includes(ev.data.nme);
     let flds = isPlainText
         ? [{ name: 'txt', label: 'Text', type: 'text', value: frmct.text() }]
         : [{ name: 'txt', label: 'Text', type: 'html', value: frmct.html(), tinymce: true, attr: { style: 'height: 300px' } }];
@@ -1027,6 +1394,11 @@ $inv.eHtml = function (ev) {
             if (typeof change === 'function') {
                 change(response.txt);
             }
+            /* backend-authoritative: mirror the inline recipient-field edit to the server session.
+               Invoice and reminder editors share this DOM; each syncField no-ops unless its own
+               draft token is present, so only the active mode's session receives the delta. */
+            $inv.d.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
+            $inv.rd.syncField(ev.data.nme, isPlainText ? (response.txt || '') : response.txt);
         },
         tinymce: { valid_elements: 'br', hidemenu: true, hidetoolbar: true }
     }
@@ -1112,7 +1484,11 @@ $inv.eRw = function(row, dta, flds) {
         }, typedvalues: true
     });
 };
-$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', swapdone: (p1, p2, i1, i2) => { $inv.t_fds_inv(); } }) }
+/* Reorder items via drag. The DOM swap happens inside the Sortable during the drag; we commit
+   the new order once, reliably, on drop (onend) — that recomputes positions/totals and pushes the
+   changed block(s) to the backend session (t_fds_inv -> syncChanged). Committing on drop (rather
+   than on every mid-drag hover-swap) avoids rebuilding the row that is currently being dragged. */
+$inv.bdysort = (i, e) => { $(e).Sortable({ dragItem: false, dragHandleClass: 'ico', parentident: 'tr', onend: () => { $inv.t_fds_inv(); } }) }
 $inv.rrw = function () {
     let rw = $(this), dta = rw.data(), co = {}, ph = rw.is('.placeholder'), hn = rw.is('.hidenote');
     let oHtml = (e) => $$.d().append(e).html();
@@ -1241,6 +1617,13 @@ $inv.invSumUpdate = function () {
     }
     tbl.data('sms', sms);
     tbl.data('bai', ba);
+    /* Backend-authoritative seeding (ADR 0006): on the first calculation of an invoice
+       draft (invSumUpdate is only bound for invoices, never reminders), hand the assembled
+       model to the server session and switch to server-driven totals from then on. */
+    if ((tbl.data('dtoken') || '') === '' && bool(tbl.data('dseeding'), false) === false && ((tbl.data('admin') || {}).type != null)) {
+        tbl.data('dseeding', true);
+        $inv.d.seed($.extend($inv.invcPayload(tbl.data()), { invid: tbl.data('invid') || '' }));
+    }
 };
 $inv.worknotes = function (rx) {
     let wn = '';
@@ -1328,7 +1711,13 @@ $inv.rendersrq = function () {
         $$.tdc('currency isumval', istr);
     }
 };
-$inv.t_fds_inv = () => { $('div.invoice_layout table.invi').trigger('fds.inv'); };
+$inv.t_fds_inv = () => {
+    let tbl = $('div.invoice_layout table.invi');
+    tbl.trigger('fds.inv');
+    /* After any local item mutation, push the changed block(s) to the authoritative
+       server session as granular deltas (invoice drafts only — reminders have no token). */
+    if ((tbl.data('dtoken') || '') !== '') { $inv.d.syncChanged(tbl); }
+};
 $inv.sedit = () => {
     $inv.sprev(true);
 };
@@ -1383,6 +1772,7 @@ $inv.sp13b = () => {
     } else {
     }
     tbl.trigger('fds.inv');
+    $inv.d.sync({ Target: 'p13b', Value: d.admin.p13b });
 };
 /* Maps an item row's data to the backend item contract consumed by InvoiceSetPricing
    / FuchsPdf.ApplyInvoice: { id, type, title (plain), desc (html), qty, price_net,
@@ -1437,6 +1827,7 @@ $inv.setSetmode = (mode) => {
     let opts = (d.inv.InvoiceOptions || '').split(',').filter(x => x !== '' && x.indexOf('setmode:') !== 0);
     if (mode && mode !== 'setprice') { opts.push('setmode:' + mode); }
     d.inv.InvoiceOptions = opts.join(',');
+    $inv.d.sync({ Target: 'setmode', Value: mode });
 };
 $inv.sctp = () => {
     let flds = $invcol.ctp;
@@ -1453,6 +1844,7 @@ $inv.sctp = () => {
             cvo.contactEmail = response.email;
             d.new.CustomValues = JSON.stringify(cvo);  //Assign it to new Values so that this is submitted also
             l.find('.ctpfrm').text(ne(response.name, response.email));
+            $inv.d.sync({ Target: 'contact', Value: { name: response.name, email: response.email } });
 
         }, typedvalues: true
     });
@@ -1477,82 +1869,12 @@ $inv.invcPayload = function (d) {
     adm.customerid = (adm.customerid != null ? adm.customerid : adm.CustomerId);
     return { admin: adm, req: d.bai, sms: d.sms, new: nw };
 };
-$inv.ssave = () => {
+/* Zwischenspeichern and preview now run against the backend-authoritative session
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
+   (ADR 0006): no full-invoice re-upload — the cached draft is flushed / rendered by
-    $inv.t_fds_inv();
+   token. See $inv.d.save / $inv.d.preview. The finalise + email path (req/sconf) is
-    l.aC('freeze');
+   unchanged and is invoked from the preview modal's confirm handler. */
-    $ocms.postXT({
+$inv.ssave = () => { $inv.d.save(); };
-        url: $ocms.url('req/save'), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid || '' }, success: (response) => {
+$inv.sprev = (change) => { $inv.d.preview(); };
-            $inv.cntInv({ id: response.id });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
-$inv.sprev = (change) => {
-    var l = $('div.invoice_layout'), d = l.find('table.invi').data();
-    change = bool(change, false);
-    $inv.t_fds_inv();
-    l.aC('freeze');
-    //console.debug({ admin: d.admin, req: d.bai, sms: d.sms, new: d.new });
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc),false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('req/' + (change === true ?'sedit':'sprep')), data: { invc: JSON.stringify($inv.invcPayload(d)), id: d.invid ||'' }, success: (response) => {
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), invid = response.id, invtp = response.total;
-            if (invtp > 10) {
-                $$.dc('note warn', c).text($ict.tpe);
-            }
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            for (let ic = (response.img || []).length + 1; ic <= invtp; ic++) {
-                $$.dc('pdfp ph', c).append($$.dc('note', $ict.pna));
-            }
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $rct.crI, confirm: function (e) {
-                    let ct = $(this);
-                    l.aC('freeze');  /* spinner while the invoice is finalized/emailed on the backend */
-                    $ocms.postXT({
-                        url: $ocms.url('req/sconf'), data: { id: invid }, success: (cresp) => {
-                            ct.trigger('modal_close');
-                            if (cresp.hasFile === true) {
-                                window.open($ocms.url('req/idoc') + '?id=' + invid, '_blank');  /* open pdf in new tab, only if a file was actually created */
-                            }
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }, complete: () => {
-                            l.rC('freeze');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('req/sdel'), data: {
-                                id: invid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }, error: () => {
-            alert($ict.eis);
-        }, complete: () => {
-            l.rC('freeze');
-        }
-    });
-};
 $inv.rReload = () => {
     try {
         let s = $('#listframe ul.rql:first').data();
@@ -1731,6 +2053,8 @@ $inv.eRowR = function (ev) {
             $.extend(tdta.rm, res);
             tbl.data(tdta);
             $inv.rRemRw.call(row, tdta);
+            /* backend-authoritative: mirror the edited amount / amount-paid to the server session */
+            $inv.rd.syncAmount(tdta.rm.amount, tdta.rm.amount_payed);
         }, typedvalues: true
     });
 };
@@ -1771,57 +2095,26 @@ $inv.ccRem_s2 = function (id, sets) {  //reminder creation
             rif.tbl.children('tbody').each($inv.bdysort);
             rif.tbl.trigger('fds.inv');  /* trigger calculations */
 
+            /* Seed the authoritative server session (ADR 0006). Amounts join the recipient
+               fields in the 'new' block; the reference invoice data goes into 'rem'. From here
+               the backend owns the open-amount computation and validation; inline edits and the
+               item-row dialog post single deltas (see $inv.rd). */
+            let nw = rif.tbl.data('new');
+            nw.amount = rem.amount; nw.amount_payed = rem.amount_payed;
+            $inv.rd.seed({
+                rem: { invid: rem.invid, type: rem.type, invoiceid: rem.invoiceid, invoicedate: rem.invoicedate },
+                new: nw
+            });
         }, complete: () => {
             //o.c.trigger('modal_close');
         }
     });
 };
 $inv.rprev = () => {
-    var l = $('div.invoice_layout'), tbl = l.find('table.invi'), d = tbl.data();
+    /* Preview + finalise now run through the backend-authoritative session ($inv.rd):
-    $.extend(d.new, tbl.find('tbody > tr:first').data());
+       the PDF renders straight from the server cache (no rem/prep DB write), and confirm
-    l.aC('freeze');
+       flushes (rem/dsave) then finalises + emails (rem/conf). */
-    //console.debug({ rem: d.rm, new: d.new });
+    $inv.rd.preview();
-    if ($fis.ValidateEmail(d.new.invoiceemail || '') === false) {
-        if (bool(confirm($ict.ivE + $ict.ivEc), false) === false) {
-            l.rC('freeze');
-            return;
-        }
-    }
-    $ocms.postXT({
-        url: $ocms.url('rem/prep'), data: { remc: JSON.stringify({ rem: d.rm, new: d.new }), id: d.invid || '' }, success: (response) => {
-            l.rC('freeze');
-            let c = $$.dc('imagecollection pdfpreview'), vhr = Math.round(vh() * 0.88), remid = response.id;
-            $.each(response.img || [], function (ii, img) {
-                $$.dc('pdfp', c).append($$.img(img).css('max-height', (vhr - rpx(6)).toString() + 'px'));
-            });
-            $ocms.dlg(c, {
-                size: [vhr, Math.round(vw() * 0.88)], zindex: 50, form: false, button: $ict.remd, confirm: function (e) {
-                    let ct = $(this);
-                    $ocms.postXT({
-                        url: $ocms.url('rem/conf'), data: { id: remid }, success: () => {
-                            ct.trigger('modal_close');
-                            window.open($ocms.url('rem/idoc') + '?id=' + remid, '_blank');  /* open pdf in new tab */
-                            $ocms.init('req');   /* go back to request list */
-                            $inv.rReload();
-                        }, error: () => {
-                            alert($t.f1);
-                            ct.trigger('modal_close');
-                        }
-                    });
-                }, cancel: function (e) {
-                    let ct = $(this);
-                    if (confirm($ict.cdI)) {
-                        $ocms.postXT({
-                            url: $ocms.url('rem/del'), data: {
-                                id: remid
-                            }
-                        });
-                    }
-                    $inv.rReload();
-                }
-            });
-        }
-    });
 };
 $inv.sis = (id) => {
     if (confirm($ict.sisc)) {