Enhance financial report accuracy by including closing journals in profit and loss calculations and trial balances; add idempotency check for journal entry creation.

Services/JournalEntryService.cs

@@ -31,6 +31,18 @@ namespace General_Ledger_Service.Services
 
         public async Task<ApiResponse> CreateAsync(CreateJournalEntryRequest request)
         {
+            // Idempotency guard for service-to-service callers: the same sourceModule + reference is only ever
+            // posted once, so a retry after a timeout returns the existing entry instead of double-posting.
+            if (request.Correction is null
+                && !string.IsNullOrWhiteSpace(request.SourceModule) && !string.IsNullOrWhiteSpace(request.Reference))
+            {
+                var existing = await _journalEntryRepository.GetJournalEntryBySourceReferenceAsync(request.SourceModule, request.Reference);
+                if (existing is not null)
+                {
+                    return ResponseHelpers.Ok("Journal entry already exists for this sourceModule and reference", existing);
+                }
+            }
+
             var period = await _fiscalCalendarRepository.GetPeriodByIdAsync(request.PeriodId)
                 ?? throw new NotFoundException("Period not found");