update detail.

API/ROLAC.API/Services/DisbursementService.cs

@@ -40,6 +40,19 @@ public class DisbursementService : IDisbursementService
         var memberIds = rows.Where(r => r.MemberId != null).Select(r => r.MemberId!.Value).ToHashSet();
         var members = await _db.Members.AsNoTracking().Where(m => memberIds.Contains(m.Id)).ToDictionaryAsync(m => m.Id);
 
+        // Category label per expense: the single line's category, or "Multiple" when it spans several.
+        var expenseIds = rows.Select(r => r.Id).ToList();
+        var lineGroups = await _db.ExpenseLines.AsNoTracking()
+            .Where(l => expenseIds.Contains(l.ExpenseId))
+            .OrderBy(l => l.Id)
+            .Select(l => new { l.ExpenseId, l.CategoryGroupId })
+            .ToListAsync();
+        var categoryByExpense = lineGroups.GroupBy(l => l.ExpenseId).ToDictionary(
+            g => g.Key,
+            g => g.Select(l => l.CategoryGroupId).Distinct().Count() > 1
+                ? "Multiple / 多類別"
+                : grpNames.GetValueOrDefault(g.First().CategoryGroupId, ""));
+
         var groups = new Dictionary<string, PayeeGroupDto>();
         foreach (var e in rows)
         {
@@ -77,7 +90,7 @@ public class DisbursementService : IDisbursementService
                 ExpenseId = e.Id, ExpenseDate = e.ExpenseDate.ToString("yyyy-MM-dd"),
                 Description = e.Description, Amount = e.Amount,
                 MinistryName = minNames.GetValueOrDefault(e.MinistryId, ""),
-                CategoryName = grpNames.GetValueOrDefault(e.CategoryGroupId, ""),
+                CategoryName = categoryByExpense.GetValueOrDefault(e.Id, ""),
             });
             g.TotalAmount += e.Amount;
         }