Add OpenTelemetry, performance metrics, and broaden logging + tests

Observability:
- New FuchsTelemetry (ActivitySource + Meter) defining business counters
  (invoices/reminders/reports rendered, emails/sms sent+failed, MT940 rows,
  MFR calls) and duration histograms (PDF render, report render, email send).
- Program.cs wires OpenTelemetry tracing (ASP.NET Core, HttpClient, SqlClient,
  app source) and metrics (ASP.NET Core, HttpClient, runtime, app meter).
  OTLP export is enabled only when Fuchs:Telemetry:OtlpEndpoint is set, so a
  missing collector never affects the app; disable via Fuchs:Telemetry:Enabled.

Instrumentation + logging:
- Services (Pdf, Invoice, Reminder, Report, Com, Banking, Widget, MfrFactory)
  now emit spans, record metrics, and log entry/result/timing/errors.
- Added dispatch + key-action logging to the previously silent handlers
  (Banking, Reminder, Reports, Requests).

Tests (137 total, +10):
- ProcessWebComServiceTests with a stub HttpMessageHandler cover success
  (API 200), failure (API 500, invalid email, empty mobile), disabled mode,
  the base64 attachment payload contract, and metric emission via MeterListener.

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

Fuchs/Controllers/IntranetController.Banking.cs

@@ -15,12 +15,15 @@ public partial class IntranetController
 {
     private async Task<IActionResult> Do_Process_Bankings(string fn, string id, string code)
     {
+        _logger.LogDebug("Do_Process_Bankings action={Action} user={User}", id, UserAccountID);
         switch (id.ToLower())
         {
             case "auth":
                 return await JSONAsync(new { manage = 1 });
 
             case "up":
+                _logger.LogInformation("Banking MT940 upload: {FileCount} file(s) user={User}",
+                    Request.Form.Files.Count, UserAccountID);
                 foreach (var fle in Request.Form.Files)
                 {
                     using var stream = fle.OpenReadStream();
@@ -50,6 +53,8 @@ public partial class IntranetController
                     dtwa.OnCommandAfterError += (_, exc) =>
                         _intranet.debug_log("IntranetController.bam.up - command-after exception",
                             exc, UserAccountID, new { uid = dtwa.InstanceGUID, tmptbl });
+                    _logger.LogDebug("Banking upload parsed {Rows} rows → temp table submit (user={User})",
+                        tbl.Rows.Count, UserAccountID);
                     dtwa.DoSubmit();
                 }
                 return Ok();

Fuchs/Controllers/IntranetController.Reminder.cs

@@ -17,6 +17,7 @@ public partial class IntranetController
 {
     private async Task<IActionResult> Do_Process_Reminder(string fn, string id, string code)
     {
+        _logger.LogDebug("Do_Process_Reminder action={Action} user={User}", id, UserAccountID);
         switch (id.ToLower())
         {
             case "get":
@@ -117,6 +118,8 @@ public partial class IntranetController
                     frdic.no("InvoiceFile", null!) is byte[] invFile)
                     remdoc[frdic.nz("InvoiceFileName")] = invFile;
 
+                _logger.LogInformation("Reminder conf: emailing finalized reminder {RemId} to {Email} user={User}",
+                    remId, email.Trim(), UserAccountID);
                 bool sent = await _comService.SendEmailAsync(
                     $"inv_{remId}",
                     $"SanitärFuchs - {frdic.nz("subject").ne(frdic.nz("DocumentName"))}",

Fuchs/Controllers/IntranetController.Reports.cs

@@ -13,6 +13,7 @@ public partial class IntranetController
 {
     private async Task<IActionResult> Do_Process_Reports(string fn, string id, string code)
     {
+        _logger.LogDebug("Do_Process_Reports action={Action} code={Code} user={User}", id, code, UserAccountID);
         switch (id.ToLower())
         {
             case "auth":

Fuchs/Controllers/IntranetController.Requests.cs

@@ -19,6 +19,7 @@ public partial class IntranetController
 {
     private async Task<IActionResult> Do_Process_Requests(string fn, string id, string code)
     {
+        _logger.LogDebug("Do_Process_Requests action={Action} user={User}", id, UserAccountID);
         switch (id.ToLower())
         {
             case "auth":
@@ -277,6 +278,8 @@ public partial class IntranetController
                 double bal = Convert.ToDouble(frdic.no("InvoiceBalance", 0));
                 string terms = fdInv.PaymentTerms.Replace("wd", " Werktagen").Replace("d", " Tagen").Replace("wk", " Wochen").ne("10 Tagen");
                 string body  = BuildInvoiceBody(bal, terms);
+                _logger.LogInformation("Request sconf: emailing finalized invoice {InvId} to {Email} user={User}",
+                    invId, email.Trim(), UserAccountID);
                 bool sent = await _comService.SendEmailAsync(
                     $"inv_{invId}", $"Sanit\u00e4rFuchs - {frdic.nz("DocumentName")}",
                     body, email.Trim(), "", inv);

Fuchs/Fuchs.csproj

@@ -33,6 +33,12 @@
     <PackageReference Include="HtmlAgilityPack" Version="1.12.4" />
     <PackageReference Include="MailKit" Version="4.17.0" />
     <PackageReference Include="Microsoft.IO.RecyclableMemoryStream" Version="3.0.1" />
+    <PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" Version="1.15.3" />
+    <PackageReference Include="OpenTelemetry.Extensions.Hosting" Version="1.15.3" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.15.2" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.Http" Version="1.15.1" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.Runtime" Version="1.15.1" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.SqlClient" Version="1.15.2" />
     <PackageReference Include="Portable.BouncyCastle" Version="1.9.0" />
     <PackageReference Include="QRCoder" Version="1.8.0" />
 	  <PackageReference Include="PDFsharp" Version="6.2.4" />

Fuchs/Observability/FuchsTelemetry.cs

@@ -0,0 +1,56 @@
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+
+namespace Fuchs.Observability;
+
+/// <summary>
+/// Central definition of the application's OpenTelemetry instrumentation:
+/// a single <see cref="ActivitySource"/> for tracing and a single
+/// <see cref="Meter"/> with the business / performance instruments.
+///
+/// These use the in-box <c>System.Diagnostics</c> APIs, which the OpenTelemetry
+/// SDK (wired up in <c>Program.cs</c>) collects and exports. Code can therefore
+/// emit spans and metrics without taking a direct dependency on the OTel SDK.
+/// </summary>
+public static class FuchsTelemetry
+{
+    public const string ServiceName = "Fuchs.Intranet";
+    public static readonly string ServiceVersion =
+        typeof(FuchsTelemetry).Assembly.GetName().Version?.ToString() ?? "1.0.0";
+
+    /// <summary>Tracing source — register this name with the tracer provider.</summary>
+    public static readonly ActivitySource ActivitySource = new(ServiceName, ServiceVersion);
+
+    /// <summary>Metrics meter — register this name with the meter provider.</summary>
+    public static readonly Meter Meter = new(ServiceName, ServiceVersion);
+
+    // ── Business counters ────────────────────────────────────────────────────
+    public static readonly Counter<long> InvoicesRendered =
+        Meter.CreateCounter<long>("fuchs.invoices.rendered", "{invoice}", "Number of invoice PDFs rendered.");
+    public static readonly Counter<long> RemindersRendered =
+        Meter.CreateCounter<long>("fuchs.reminders.rendered", "{reminder}", "Number of reminder PDFs rendered.");
+    public static readonly Counter<long> ReportsRendered =
+        Meter.CreateCounter<long>("fuchs.reports.rendered", "{report}", "Number of reports rendered (by function).");
+    public static readonly Counter<long> EmailsSent =
+        Meter.CreateCounter<long>("fuchs.emails.sent", "{email}", "Number of emails accepted by the mailer API.");
+    public static readonly Counter<long> EmailsFailed =
+        Meter.CreateCounter<long>("fuchs.emails.failed", "{email}", "Number of emails that failed to send.");
+    public static readonly Counter<long> SmsSent =
+        Meter.CreateCounter<long>("fuchs.sms.sent", "{sms}", "Number of SMS messages sent.");
+    public static readonly Counter<long> Mt940RowsParsed =
+        Meter.CreateCounter<long>("fuchs.banking.mt940.rows", "{row}", "Number of MT940 transaction lines parsed.");
+    public static readonly Counter<long> MfrCalls =
+        Meter.CreateCounter<long>("fuchs.mfr.calls", "{call}", "Number of MFR ERP client calls initiated.");
+
+    // ── Performance histograms (durations in milliseconds) ───────────────────
+    public static readonly Histogram<double> PdfRenderDuration =
+        Meter.CreateHistogram<double>("fuchs.pdf.render.duration", "ms", "PDF render duration.");
+    public static readonly Histogram<double> ReportRenderDuration =
+        Meter.CreateHistogram<double>("fuchs.report.render.duration", "ms", "Report render duration.");
+    public static readonly Histogram<double> EmailSendDuration =
+        Meter.CreateHistogram<double>("fuchs.email.send.duration", "ms", "Email send round-trip duration.");
+
+    /// <summary>Starts a span on the application's <see cref="ActivitySource"/>.</summary>
+    public static Activity? StartActivity(string name, ActivityKind kind = ActivityKind.Internal) =>
+        ActivitySource.StartActivity(name, kind);
+}

Fuchs/Program.cs

@@ -1,5 +1,6 @@
 using Fuchs.intranet;
 using Fuchs.Logging;
+using Fuchs.Observability;
 using OCORE_web.Secrets;
 using Fuchs.Services;
 using Microsoft.AspNetCore.Authentication.Cookies;
@@ -8,6 +9,9 @@ using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.Logging;
 using OCORE.security;
 using OCORE.web;
+using OpenTelemetry.Metrics;
+using OpenTelemetry.Resources;
+using OpenTelemetry.Trace;
 
 namespace Fuchs;
 
@@ -84,6 +88,38 @@ public class Program
         builder.Services.AddScoped<IReportService, FuchsReportService>();
         builder.Services.AddScoped<IInvoiceService, InvoiceService>();
         builder.Services.AddScoped<IReminderService, ReminderService>();
+
+        // ── OpenTelemetry: tracing + metrics ─────────────────────────────────
+        // Instrumentation is always collected; OTLP export is enabled only when
+        // an endpoint is configured (Fuchs:Telemetry:OtlpEndpoint), so a missing
+        // collector never impacts the app. Disable entirely with Enabled=false.
+        bool telemetryEnabled = builder.Configuration.GetValue("Fuchs:Telemetry:Enabled", true);
+        string? otlpEndpoint  = builder.Configuration["Fuchs:Telemetry:OtlpEndpoint"];
+        if (telemetryEnabled)
+        {
+            builder.Services.AddOpenTelemetry()
+                .ConfigureResource(r => r.AddService(
+                    serviceName: FuchsTelemetry.ServiceName,
+                    serviceVersion: FuchsTelemetry.ServiceVersion))
+                .WithTracing(t =>
+                {
+                    t.AddSource(FuchsTelemetry.ServiceName)
+                     .AddAspNetCoreInstrumentation()
+                     .AddHttpClientInstrumentation()
+                     .AddSqlClientInstrumentation();
+                    if (!string.IsNullOrWhiteSpace(otlpEndpoint))
+                        t.AddOtlpExporter(o => o.Endpoint = new Uri(otlpEndpoint));
+                })
+                .WithMetrics(m =>
+                {
+                    m.AddMeter(FuchsTelemetry.ServiceName)
+                     .AddAspNetCoreInstrumentation()
+                     .AddHttpClientInstrumentation()
+                     .AddRuntimeInstrumentation();
+                    if (!string.IsNullOrWhiteSpace(otlpEndpoint))
+                        m.AddOtlpExporter(o => o.Endpoint = new Uri(otlpEndpoint));
+                });
+        }
     }
 
     private static void ConfigureApp(WebApplication app)

Fuchs/Services/BankingService.cs

@@ -1,4 +1,6 @@
 using System.Data;
+using System.Diagnostics;
+using Fuchs.Observability;
 using Microsoft.Extensions.Logging;
 using programmersdigest.MT940Parser;
 
@@ -27,6 +29,8 @@ public class BankingService : IBankingService
 
     public DataTable ParseToDatatable(Stream stream, DataTable? schemaDatatable = null)
     {
+        using var act = FuchsTelemetry.StartActivity("banking.mt940.parse");
+        var sw = Stopwatch.StartNew();
         var tbl = schemaDatatable?.Clone() ?? BuildDefaultSchema();
 
         void SetNfo(DataRow nr, string key, object? value)
@@ -94,6 +98,10 @@ public class BankingService : IBankingService
         }
 
         tbl.AcceptChanges();
+        sw.Stop();
+        FuchsTelemetry.Mt940RowsParsed.Add(tbl.Rows.Count);
+        act?.SetTag("fuchs.banking.rows", tbl.Rows.Count);
+        _logger.LogInformation("MT940 parsed {Rows} transaction lines in {Ms} ms", tbl.Rows.Count, sw.ElapsedMilliseconds);
         return tbl;
     }
 

Fuchs/Services/FuchsPdfService.cs

@@ -1,4 +1,6 @@
-using Fuchs.intranet;
+using System.Diagnostics;
+using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.Extensions.Logging;
 using MigraDoc.DocumentObjectModel;
 
@@ -6,7 +8,8 @@ namespace Fuchs.Services;
 
 /// <summary>
 /// PDF service implementation. Delegates to <see cref="FuchsPdf"/> static methods
-/// while providing a DI-friendly injectable wrapper.
+/// while providing a DI-friendly injectable wrapper, structured logging and
+/// render-duration metrics.
 /// </summary>
 public class FuchsPdfService : IPdfService
 {
@@ -16,30 +19,94 @@ public class FuchsPdfService : IPdfService
     {
         _logger = logger;
         FuchsPdf.SetLicense();
+        _logger.LogDebug("FuchsPdfService initialised (PDF license applied).");
     }
 
     public Task<Document> WriteLetterAsync(FuchsPdf.FdsTextBlocks textBlocks, bool draft)
     {
+        _logger.LogDebug("WriteLetterAsync draft={Draft}", draft);
         return FuchsPdf.WriteLetter(textBlocks, draft, FuchsPdf.DeCulture);
     }
 
     public void ApplyInvoice(Document doc, FuchsPdf.FdsTextBlocks textBlocks,
         FdsInvoiceData invoice, bool draft = false)
     {
+        _logger.LogDebug("ApplyInvoice id={Id} draft={Draft}", invoice.Id, draft);
         FuchsPdf.ApplyInvoice(doc, textBlocks, invoice, draft);
     }
 
     public void ApplyReminder(Document doc, FuchsPdf.FdsTextBlocks textBlocks,
         FdsReminderData reminder, bool draft = false)
     {
+        _logger.LogDebug("ApplyReminder id={Id} draft={Draft}", reminder.Id, draft);
         FuchsPdf.ApplyReminder(doc, textBlocks, reminder, draft);
     }
 
-    public byte[] DocToPdfBytes(Document doc) => FuchsPdf.DocToPdfBytes(doc);
+    public byte[] DocToPdfBytes(Document doc)
+    {
+        var sw = Stopwatch.StartNew();
+        using var act = FuchsTelemetry.StartActivity("pdf.render");
+        try
+        {
+            byte[] bytes = FuchsPdf.DocToPdfBytes(doc);
+            sw.Stop();
+            FuchsTelemetry.PdfRenderDuration.Record(sw.Elapsed.TotalMilliseconds,
+                new KeyValuePair<string, object?>("operation", "pdf"));
+            act?.SetTag("fuchs.pdf.bytes", bytes.Length);
+            _logger.LogDebug("DocToPdfBytes rendered {Bytes} bytes in {Ms} ms", bytes.Length, sw.ElapsedMilliseconds);
+            return bytes;
+        }
+        catch (Exception ex)
+        {
+            sw.Stop();
+            act?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            _logger.LogError(ex, "DocToPdfBytes failed after {Ms} ms", sw.ElapsedMilliseconds);
+            throw;
+        }
+    }
 
-    public Task<OCORE.pdf._pdf.ImageCollection> DocToImageCollectionAsync(Document doc) =>
-        FuchsPdf.DocToImageCollection(doc);
+    public async Task<OCORE.pdf._pdf.ImageCollection> DocToImageCollectionAsync(Document doc)
+    {
+        var sw = Stopwatch.StartNew();
+        using var act = FuchsTelemetry.StartActivity("pdf.render.images");
+        try
+        {
+            var col = await FuchsPdf.DocToImageCollection(doc);
+            sw.Stop();
+            FuchsTelemetry.PdfRenderDuration.Record(sw.Elapsed.TotalMilliseconds,
+                new KeyValuePair<string, object?>("operation", "images"));
+            act?.SetTag("fuchs.pdf.pages", col.TotalPages);
+            _logger.LogDebug("DocToImageCollectionAsync rendered {Pages} pages in {Ms} ms", col.TotalPages, sw.ElapsedMilliseconds);
+            return col;
+        }
+        catch (Exception ex)
+        {
+            sw.Stop();
+            act?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            _logger.LogError(ex, "DocToImageCollectionAsync failed after {Ms} ms", sw.ElapsedMilliseconds);
+            throw;
+        }
+    }
 
-    public Task<OCORE.pdf._pdf.ImageCollection> BytesToImageCollectionAsync(byte[] pdfBytes) =>
-        FuchsPdf.BytesToImageCollection(pdfBytes);
+    public async Task<OCORE.pdf._pdf.ImageCollection> BytesToImageCollectionAsync(byte[] pdfBytes)
+    {
+        var sw = Stopwatch.StartNew();
+        using var act = FuchsTelemetry.StartActivity("pdf.bytes.images");
+        try
+        {
+            var col = await FuchsPdf.BytesToImageCollection(pdfBytes);
+            sw.Stop();
+            FuchsTelemetry.PdfRenderDuration.Record(sw.Elapsed.TotalMilliseconds,
+                new KeyValuePair<string, object?>("operation", "bytes-images"));
+            _logger.LogDebug("BytesToImageCollectionAsync rendered {Pages} pages in {Ms} ms", col.TotalPages, sw.ElapsedMilliseconds);
+            return col;
+        }
+        catch (Exception ex)
+        {
+            sw.Stop();
+            act?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            _logger.LogError(ex, "BytesToImageCollectionAsync failed after {Ms} ms", sw.ElapsedMilliseconds);
+            throw;
+        }
+    }
 }

Fuchs/Services/FuchsReportService.cs

@@ -1,4 +1,6 @@
+using System.Diagnostics;
 using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Data.SqlClient;
 using Microsoft.Extensions.Logging;
@@ -69,6 +71,12 @@ public class FuchsReportService : IReportService
         }
         bool ciForce = prms.TryGetValue("cache", out var ca) && ca.ToLower() == "0";
 
+        var sw = Stopwatch.StartNew();
+        using var act = FuchsTelemetry.StartActivity("report.process");
+        act?.SetTag("fuchs.report.fn", tgt);
+        act?.SetTag("fuchs.report.id", report);
+        _logger.LogInformation("Report request fnc={Fnc} report={Report} tgt={Tgt} cache={Cache} user={User}",
+            fnc, report, tgt, ciCache, userAccountId);
         try
         {
             switch (tgt)
@@ -119,9 +127,18 @@ public class FuchsReportService : IReportService
         }
         catch (Exception ex)
         {
+            act?.SetStatus(ActivityStatusCode.Error, ex.Message);
             _logger.LogError(ex, "Report processing failed fnc={Fnc} report={Report} tgt={Tgt}", fnc, report, tgt);
             return new StatusCodeResult(500);
         }
+        finally
+        {
+            sw.Stop();
+            FuchsTelemetry.ReportRenderDuration.Record(sw.Elapsed.TotalMilliseconds,
+                new KeyValuePair<string, object?>("fn", tgt));
+            FuchsTelemetry.ReportsRendered.Add(1, new KeyValuePair<string, object?>("fn", tgt));
+            _logger.LogDebug("Report request completed tgt={Tgt} report={Report} in {Ms} ms", tgt, report, sw.ElapsedMilliseconds);
+        }
     }
 
     private static void ApplyReload(FuchsHtmlPage page, IDictionary<string, string> prms, int ciRefresh)

Fuchs/Services/FuchsWidgetService.cs

@@ -1,4 +1,5 @@
 using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Logging;
@@ -31,17 +32,24 @@ public class FuchsWidgetService : IWidgetService
     public async Task<IActionResult> GetWidgetAsync(string widgetId, string userAccountId,
         DatabaseSecurity dbSec, HttpRequest request)
     {
+        using var act = FuchsTelemetry.StartActivity("widget.get");
+        act?.SetTag("fuchs.widget.id", widgetId);
+        _logger.LogDebug("GetWidgetAsync widget={WidgetId} user={User}", widgetId, userAccountId);
         try
         {
-            return widgetId.ToLower() switch
+            var result = widgetId.ToLower() switch
             {
                 "my"  => await HandleWidgetMy(userAccountId, dbSec),
                 "one" => await HandleWidgetOne(userAccountId, dbSec, request),
                 _     => await HandleWidgetGeneric(widgetId, userAccountId, dbSec)
             };
+            _logger.LogDebug("GetWidgetAsync widget={WidgetId} result={Result} user={User}",
+                widgetId, result.GetType().Name, userAccountId);
+            return result;
         }
         catch (Exception ex)
         {
+            act?.SetStatus(System.Diagnostics.ActivityStatusCode.Error, ex.Message);
             _logger.LogError(ex, "Widget error for {WidgetId}, user {UserAccountId}", widgetId, userAccountId);
             return new StatusCodeResult(500);
         }

Fuchs/Services/InvoiceService.cs

@@ -1,5 +1,7 @@
 using System.Data;
+using System.Diagnostics;
 using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.Data.SqlClient;
 using Microsoft.Extensions.Logging;
 using MigraDoc.DocumentObjectModel;
@@ -33,8 +35,9 @@ public class InvoiceService : IInvoiceService
 
     public async Task<FdsInvoiceData> LoadInvoiceAsync(string id, string userAccountId, DatabaseSecurity dbSec)
     {
+        _logger.LogDebug("LoadInvoiceAsync id={Id} user={User}", id, userAccountId);
         var inv = new FdsInvoiceData();
-        if (string.IsNullOrEmpty(id)) return inv;
+        if (string.IsNullOrEmpty(id)) { _logger.LogWarning("LoadInvoiceAsync called with empty id (user={User})", userAccountId); return inv; }
 
         var pl = new List<SqlParameter>
         {
@@ -51,13 +54,15 @@ 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);
         return inv;
     }
 
     public async Task<FdsInvoiceData> RegisterInvoiceAsync(FdsInvoiceData invoice, bool change, string invId,
         string userAccountId, DatabaseSecurity dbSec)
     {
-        if (invoice.NewValues == null) return invoice;
+        _logger.LogInformation("RegisterInvoiceAsync change={Change} invId={InvId} user={User}", change, invId, userAccountId);
+        if (invoice.NewValues == null) { _logger.LogWarning("RegisterInvoiceAsync: no form values supplied (user={User})", userAccountId); return invoice; }
 
         var pl = new List<SqlParameter> { SQL_VarChar("@authuser", userAccountId) };
         pl.AddRange(invoice.BuildInvoiceParams(change, invId));
@@ -88,11 +93,16 @@ public class InvoiceService : IInvoiceService
             _logger.LogError("RegisterInvoiceAsync sql exception: {Ex}", invdset.Exception);
 
         invoice.InvoiceRegistration = new GenericObjectDictionary(invdset.Table("inv").FirstRow.toObjectDictionary());
+        _logger.LogInformation("RegisterInvoiceAsync registered id={Id} (change={Change})", invoice.Id, change);
         return invoice;
     }
 
     public Document GenerateInvoicePdf(FdsInvoiceData invoice, bool draft)
     {
+        using var act = FuchsTelemetry.StartActivity("invoice.render");
+        act?.SetTag("fuchs.invoice.id", invoice.Id);
+        act?.SetTag("fuchs.invoice.draft", draft);
+        _logger.LogDebug("GenerateInvoicePdf id={Id} draft={Draft}", invoice.Id, draft);
         var reg = invoice.InvoiceRegistration;
         var tb = new FuchsPdf.FdsTextBlocks
         {
@@ -108,6 +118,7 @@ public class InvoiceService : IInvoiceService
         var doc = _pdf.WriteLetterAsync(tb, draft).GetAwaiter().GetResult();
         doc.Info.Title = reg?.getString("InvoiceTitle") ?? "";
         _pdf.ApplyInvoice(doc, tb, invoice, draft);
+        FuchsTelemetry.InvoicesRendered.Add(1, new KeyValuePair<string, object?>("draft", draft));
         return doc;
     }
 

Fuchs/Services/MfrClientFactory.cs

@@ -1,22 +1,28 @@
-using Microsoft.Extensions.Logging;
+using Fuchs.Observability;
+using Microsoft.Extensions.Logging;
 
 namespace Fuchs.Services;
 
 /// <summary>
 /// Factory implementation for <see cref="fds.FdsMfrClient"/>.
-/// Centralizes MFR client creation and supplies logger from DI.
+/// Centralizes MFR client creation, supplies the logger from DI, and counts
+/// client instantiations as a proxy for MFR ERP interactions.
 /// </summary>
 public class MfrClientFactory : IMfrClientFactory
 {
     private readonly ILoggerFactory _loggerFactory;
+    private readonly ILogger<MfrClientFactory> _logger;
 
     public MfrClientFactory(ILoggerFactory loggerFactory)
     {
         _loggerFactory = loggerFactory;
+        _logger = loggerFactory.CreateLogger<MfrClientFactory>();
     }
 
     public fds.FdsMfrClient Create()
     {
+        FuchsTelemetry.MfrCalls.Add(1);
+        _logger.LogDebug("Creating new FdsMfrClient instance.");
         return new fds.FdsMfrClient(_loggerFactory);
     }
 }

Fuchs/Services/ProcessWebComService.cs

@@ -1,6 +1,8 @@
-using System.Net.Http.Headers;
+using System.Diagnostics;
+using System.Net.Http.Headers;
 using System.Text;
 using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.Data.SqlClient;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -43,9 +45,13 @@ public class ProcessWebComService : IComService
     public async Task<bool> SendEmailAsync(string reference, string subject, string html,
         string email, string name, Dictionary<string, byte[]>? attachments = null)
     {
+        using var act = FuchsTelemetry.StartActivity("email.send");
+        act?.SetTag("fuchs.email.ref", reference);
         if (!IsValidEmail(email))
         {
             _logger.LogWarning("SendEmailAsync: invalid email address '{Email}' for ref {Reference}", email, reference);
+            FuchsTelemetry.EmailsFailed.Add(1, new KeyValuePair<string, object?>("reason", "invalid-email"));
+            act?.SetStatus(ActivityStatusCode.Error, "invalid-email");
             return false;
         }
 
@@ -57,12 +63,14 @@ public class ProcessWebComService : IComService
                 "[ComService DISABLED] Would send email ref={Reference} subject='{Subject}' to={Email}",
                 reference, subject, email);
             await WriteAuditLogAsync(reference, "", "", default, false, ["Service disabled – email not sent"]);
+            FuchsTelemetry.EmailsFailed.Add(1, new KeyValuePair<string, object?>("reason", "disabled"));
             return false;
         }
 
         bool success = false;
         string messageId = "";
         var errors = new List<string>();
+        var sw = Stopwatch.StartNew();
 
         try
         {
@@ -105,9 +113,18 @@ public class ProcessWebComService : IComService
         catch (Exception ex)
         {
             errors.Add("Beim Versenden ist ein Fehler aufgetreten.");
+            act?.SetStatus(ActivityStatusCode.Error, ex.Message);
             _logger.LogError(ex, "SendEmailAsync failed for {Reference}", reference);
         }
 
+        sw.Stop();
+        FuchsTelemetry.EmailSendDuration.Record(sw.Elapsed.TotalMilliseconds,
+            new KeyValuePair<string, object?>("success", success));
+        if (success) FuchsTelemetry.EmailsSent.Add(1);
+        else         FuchsTelemetry.EmailsFailed.Add(1, new KeyValuePair<string, object?>("reason", "api-error"));
+        _logger.LogInformation("SendEmailAsync ref={Reference} success={Success} in {Ms} ms",
+            reference, success, sw.ElapsedMilliseconds);
+
         await WriteAuditLogAsync(reference, messageId, "", success ? DateTime.UtcNow : default, success, errors);
         return success;
     }
@@ -138,7 +155,12 @@ public class ProcessWebComService : IComService
             };
 
             var (ok, responseBody) = await PostToApiAsync("push_com", payload);
-            if (ok) return true;
+            if (ok)
+            {
+                FuchsTelemetry.SmsSent.Add(1);
+                _logger.LogInformation("SendSmsAsync sent to {Mobile}", mobile);
+                return true;
+            }
 
             _logger.LogWarning("SendSmsAsync API error for {Mobile}: {Body}", mobile, responseBody);
             return false;

Fuchs/Services/ReminderService.cs

@@ -1,5 +1,7 @@
 using System.Data;
+using System.Diagnostics;
 using Fuchs.intranet;
+using Fuchs.Observability;
 using Microsoft.Data.SqlClient;
 using Microsoft.Extensions.Logging;
 using MigraDoc.DocumentObjectModel;
@@ -33,8 +35,9 @@ public class ReminderService : IReminderService
 
     public async Task<FdsReminderData> LoadReminderAsync(string id, string userAccountId, DatabaseSecurity dbSec)
     {
+        _logger.LogDebug("LoadReminderAsync id={Id} user={User}", id, userAccountId);
         var rem = new FdsReminderData();
-        if (string.IsNullOrEmpty(id)) return rem;
+        if (string.IsNullOrEmpty(id)) { _logger.LogWarning("LoadReminderAsync called with empty id (user={User})", userAccountId); return rem; }
 
         var pl = new List<SqlParameter>
         {
@@ -57,7 +60,8 @@ public class ReminderService : IReminderService
     public async Task<FdsReminderData> RegisterReminderAsync(FdsReminderData reminder, bool change, string remId,
         string userAccountId, DatabaseSecurity dbSec)
     {
-        if (reminder.Rem == null || reminder.Rem.Count == 0) return reminder;
+        _logger.LogInformation("RegisterReminderAsync change={Change} remId={RemId} user={User}", change, remId, userAccountId);
+        if (reminder.Rem == null || reminder.Rem.Count == 0) { _logger.LogWarning("RegisterReminderAsync: no form values supplied (user={User})", userAccountId); return reminder; }
 
         var pl = new List<SqlParameter>
         {
@@ -85,11 +89,16 @@ public class ReminderService : IReminderService
             _logger.LogError("RegisterReminderAsync sql exception: {Ex}", remdset.Exception);
 
         reminder.ReminderRegistration = new GenericObjectDictionary(remdset.Table("rem").FirstRow.toObjectDictionary());
+        _logger.LogInformation("RegisterReminderAsync registered id={Id}", reminder.Id);
         return reminder;
     }
 
     public Document GenerateReminderPdf(FdsReminderData reminder, bool draft)
     {
+        using var act = FuchsTelemetry.StartActivity("reminder.render");
+        act?.SetTag("fuchs.reminder.id", reminder.Id);
+        act?.SetTag("fuchs.reminder.draft", draft);
+        _logger.LogDebug("GenerateReminderPdf id={Id} draft={Draft}", reminder.Id, draft);
         var tb = new FuchsPdf.FdsTextBlocks
         {
             AdminRef        = "",
@@ -112,6 +121,7 @@ public class ReminderService : IReminderService
         var doc = _pdf.WriteLetterAsync(tb, draft).GetAwaiter().GetResult();
         doc.Info.Title = reminder.ReminderTitle;
         _pdf.ApplyReminder(doc, tb, reminder, draft);
+        FuchsTelemetry.RemindersRendered.Add(1, new KeyValuePair<string, object?>("draft", draft));
         return doc;
     }
 

Fuchs/appsettings.json

@@ -38,6 +38,10 @@
       "AccountId": "",
       "Token": "MANAGED_BY_KEYVAULT",
       "Enabled": false
+    },
+    "Telemetry": {
+      "Enabled": true,
+      "OtlpEndpoint": ""
     }
   }
 }