fix(giving): map duplicate-date race to 409 + return zelle/paypal refs in session detail

API/ROLAC.API/Services/OfferingSessionService.cs

@@ -57,6 +57,10 @@ public class OfferingSessionService : IOfferingSessionService
     public async Task<bool> DateExistsAsync(DateOnly date)
         => await _db.OfferingSessions.AnyAsync(s => s.SessionDate == date);
 
+    // Distinguishes a unique-index collision on SessionDate (concurrent insert) from other DB errors.
+    private async Task<bool> DateExistsConcurrentlyAsync(DateOnly date, int excludeId)
+        => await _db.OfferingSessions.AsNoTracking().AnyAsync(s => s.SessionDate == date && s.Id != excludeId);
+
     public async Task<OfferingSessionDto?> GetByIdAsync(int id)
     {
         var s = await _db.OfferingSessions.AsNoTracking().FirstOrDefaultAsync(x => x.Id == id);
@@ -84,7 +88,10 @@ public class OfferingSessionService : IOfferingSessionService
                 GivingCategoryId = l.GivingCategoryId,
                 CategoryName = catNames.TryGetValue(l.GivingCategoryId, out var cn) ? cn : "",
                 Amount = l.Amount, PaymentMethod = l.PaymentMethod,
-                CheckNumber = l.CheckNumber, IsAnonymous = l.IsAnonymous, Notes = l.Notes,
+                CheckNumber = l.CheckNumber,
+                ZelleReferenceCode = l.ZelleReferenceCode,
+                PayPalTransactionId = l.PayPalTransactionId,
+                IsAnonymous = l.IsAnonymous, Notes = l.Notes,
             }).ToList(),
         };
     }
@@ -106,7 +113,16 @@ public class OfferingSessionService : IOfferingSessionService
             Givings = r.Givings.Select(line => MapLine(line, r.SessionDate)).ToList(),
         };
         _db.OfferingSessions.Add(session);
-        await _db.SaveChangesAsync();
+        try
+        {
+            await _db.SaveChangesAsync();
+        }
+        catch (DbUpdateException)
+        {
+            if (await DateExistsConcurrentlyAsync(r.SessionDate, session.Id))
+                throw new InvalidOperationException($"An offering session for {r.SessionDate:yyyy-MM-dd} already exists.");
+            throw;
+        }
         return session.Id;
     }