fix(drafts): serialize draft session flushes and register reminders via fds__setReminder

Make invoice/reminder live-draft edits concurrency-safe with an explicit
DraftFlushResult, add the fds__setReminder stored procedure, and harden the
date helper functions. Includes concurrency and SQL contract tests.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Fuchs_Database/FuchsDatabase.sqlproj

@@ -358,6 +358,7 @@
     <Build Include="dbo\Stored Procedures\fds__createStorno_simple.sql" />
     <Build Include="dbo\Stored Procedures\fds__createStorno_copy.sql" />
     <Build Include="dbo\Stored Procedures\fds__createReminder.sql" />
+    <Build Include="dbo\Stored Procedures\fds__setReminder.sql" />
     <Build Include="dbo\Stored Procedures\fds__createInvoice_ServiceRequest.sql" />
     <Build Include="dbo\Stored Procedures\fds__createInvoice_Details.sql" />
     <Build Include="dbo\Stored Procedures\fds__createInvoice.sql" />

Fuchs_Database/dbo/Functions/AddBusinessDays.sql

@@ -1,5 +1,9 @@
-CREATE FUNCTION[dbo].[AddBusinessDays](@Date DATE,@n INT)
-RETURNS DATE AS 
+-- INLINE = OFF: scalar UDF inlining of this @@DATEFIRST arithmetic (reached via date_add /
+-- date_addcustom) killed dashboard widget queries with error 596 ("session is in the kill state").
+CREATE FUNCTION[dbo].[AddBusinessDays](@Date DATE,@n INT)
+RETURNS DATE
+WITH INLINE = OFF
+AS
 BEGIN
 DECLARE @d INT,@f INT,@DW INT;
 SET @f=CAST(abs(1^SIGN(DATEPART(DW, @Date)-(7-@@DATEFIRST))) AS BIT)

Fuchs_Database/dbo/Functions/date_add.sql

@@ -2,6 +2,9 @@
 -- Author:		<Author,,Name>
 -- Create date: <Create Date, ,>
 -- Description:	<Description, ,>
+--              INLINE = OFF: scalar UDF inlining of this IF/nested-UDF body (-> AddBusinessDays)
+--              killed the dashboard widget queries with error 596 ("session is in the kill
+--              state", class 21). Called with constant arguments, so per-row cost is negligible.
 -- =============================================
 CREATE FUNCTION [dbo].[date_add]
 (
@@ -10,6 +13,7 @@ CREATE FUNCTION [dbo].[date_add]
 	,@shift_to_first bit = 1
 )
 RETURNS date
+WITH INLINE = OFF
 AS
 BEGIN
 	DECLARE @Ret date = @date;

Fuchs_Database/dbo/Functions/date_addcustom.sql

@@ -2,6 +2,8 @@
 -- Author:		<Author,,Name>
 -- Create date: <Create Date, ,>
 -- Description:	<Description, ,>
+--              INLINE = OFF: scalar UDF inlining (nested -> AddBusinessDays) killed the dashboard
+--              widget queries with error 596 ("session is in the kill state", class 21).
 -- =============================================
 CREATE FUNCTION [dbo].[date_addcustom]
 (
@@ -9,6 +11,7 @@ CREATE FUNCTION [dbo].[date_addcustom]
 	,@phrase varchar(10)
 )
 RETURNS date
+WITH INLINE = OFF
 AS
 BEGIN
 	DECLARE @returndate date, @numpart integer = TRY_PARSE(left(@phrase, patindex('%[^0-9]%', @phrase + '.') - 1) as integer), @defpart varchar(10) = LOWER(RIGHT(@phrase, LEN(@phrase) - patindex('%[^0-9]%', @phrase + '.') + 1));

Fuchs_Database/dbo/Stored Procedures/fds__setReminder.sql

@@ -0,0 +1,66 @@
+-- =============================================
+-- Description:	Updates an unfinalised reminder draft in place ("Zwischenspeichern" of a draft
+--              that fds__createReminder already registered) — the reminder counterpart of
+--              fds__setInvoice. Only a draft that is not finalised and has no stored file is
+--              touched; otherwise no row is updated, @Id stays NULL and the caller reports the
+--              save as failed instead of silently doing nothing. The reminder stays bound to its
+--              invoice: @InvId is not updatable.
+--              Returns the same single row shape as fds__createReminder.
+-- =============================================
+CREATE PROCEDURE [dbo].[fds__setReminder]
+	@RemId varchar(10)
+	, @type varchar(3)
+	, @amount numeric(10,3)
+	, @amount_payed numeric(10,3)
+	, @SendToAddress [nvarchar](1000)
+	, @SendToEmail [nvarchar](255)
+	, @subject nvarchar(255)
+	, @text nvarchar(2000)
+	, @authuser varchar(25)
+	, @Id varchar(10) OUT
+AS
+BEGIN
+	SET NOCOUNT ON;
+
+	IF [dbo].[fis_getModuleAuth]('fds_reminder', @authuser) < 2
+		THROW 60000, N'not authorized', 1;
+
+	INSERT INTO [dbo].[fds__admin_activity] ([activity] ,[authuser] ,[info])
+		VALUES ('fds__setReminder' ,@authuser , 'remid: ' + ISNULL(@RemId, ''));
+
+	DECLARE @now datetime = GETUTCDATE();
+	DECLARE @OUT [dbo].[fds__tt__reminder_core];
+
+	UPDATE [dbo].[fds__reminder]
+	   SET [Version]       = [Version] + 1
+	      ,[type]          = ISNULL(@type, [type])
+	      ,[amount]        = @amount
+	      ,[amount_payed]  = @amount_payed
+	      ,[SendToAddress] = @SendToAddress
+	      ,[SendToEmail]   = @SendToEmail
+	      ,[subject]       = @subject
+	      ,[text]          = @text
+	      ,[DateModified]  = @now
+	      ,[UserModified]  = @authuser
+	OUTPUT inserted.*
+		INTO @OUT
+	 WHERE [Id] = @RemId
+	   AND [DateFinalized] IS NULL   -- IsFinal = 0
+	   AND [file] IS NULL;
+
+	SELECT TOP(1) @Id = [Id] FROM @OUT;   -- stays NULL when nothing matched
+
+	With inv as(
+		select TOP(1) * FROM [dbo].[fds__invoices] WHERE [id] = (SELECT TOP(1) [InvId] FROM @OUT)
+	)
+	SELECT TOP(1)
+		o.*
+	  , [InvoiceId]			= inv.[InvoiceId]
+	  , [InvoiceDate]		= [dbo].[fds__fn_invoiceDate](inv.[DateFinalized], inv.[DateCreated])
+	  , [hasFile]			= CAST (  CASE WHEN o.[file] is null THEN 0 ELSE 1 END as bit)
+	  , [UserNameFinalized]	=  [dbo].[fis_admin_getUserName_byID](o.[UserFinalized])
+	  , [UserEmailFinalized] =  [dbo].[fis_admin_getUserEmail_byID](o.[UserFinalized])
+	from @OUT as o
+		join inv on o.[InvId] = inv.[Id];
+
+END