update detail.

API/ROLAC.API/Entities/ExpenseLine.cs

@@ -0,0 +1,23 @@
+using ROLAC.API.Entities.Base;
+namespace ROLAC.API.Entities;
+
+/// <summary>
+/// One category line of an <see cref="Expense"/>. A single invoice/payment can span
+/// multiple expense categories, so the category / amount / functional-class axis lives
+/// here per line; the Expense header keeps payment-level info and a denormalized total.
+/// Lines are wholly owned by the header (replaced as a set on update, like CheckLine).
+/// </summary>
+public class ExpenseLine : AuditableEntity
+{
+    public int      Id              { get; set; }
+    public int      ExpenseId       { get; set; }
+    public int      CategoryGroupId { get; set; }
+    public int      SubCategoryId   { get; set; }
+    public string?  FunctionalClass { get; set; }   // null = inherit Ministry.DefaultFunctionalClass
+    public decimal  Amount          { get; set; }
+    public string?  Description     { get; set; }    // optional per-line note (header description is authoritative for check printing)
+
+    public Expense?              Expense       { get; set; }
+    public ExpenseCategoryGroup? CategoryGroup { get; set; }
+    public ExpenseSubCategory?   SubCategory   { get; set; }
+}