fix(train-scheduling): move loose wagons and locomotives on train merge

apps/edr-freight-api/src/modules/train-scheduling/utils/schedule-wagon-usage.util.spec.ts

@@ -68,6 +68,23 @@ describe('computeScheduleWagonUsage', () => {
     expect(usage.wagonsRemaining).toBe(0);
   });
 
+  it('sells against the planned ceiling, not the partially coupled consist', () => {
+    // S-2026-00003: planned 3 wagons, 2 coupled + allocated for a paid booking
+    // that reserved 2 — the list read "2/2 used, 0 bookable" while the detail
+    // page and the booking gate (remainingWagonsForLeg vs maxWagons) both said
+    // 1 wagon was still free. Wagons couple on demand; the ceiling is capacity.
+    const usage = computeScheduleWagonUsage({
+      wagonSlots: Array(2).fill(slot(true)),
+      storedWagonCount: 2,
+      scheduleBookings: [booking(2)],
+      maxWagons: 3,
+    });
+
+    expect(usage.wagonsUsed).toBe(2);
+    expect(usage.wagonsTotal).toBe(3);
+    expect(usage.wagonsRemaining).toBe(1);
+  });
+
   it('falls back to the stored counter when slot rows were not loaded', () => {
     const usage = computeScheduleWagonUsage({
       wagonSlots: [],

apps/edr-freight-api/src/modules/train-scheduling/utils/schedule-wagon-usage.util.ts

@@ -20,11 +20,11 @@ export interface ScheduleBookingLike {
 export interface ScheduleWagonUsage {
   /** Coupled slots carrying at least one booking allocation. */
   wagonsUsed: number;
-  /** Coupled consist size — the denominator of `wagonsUsed`. */
+  /** Schedule capacity — the larger of coupled consist and planned ceiling. */
   wagonsTotal: number;
   /** Wagons claimed by bookings, including bookings that have not paid. */
   wagonsReserved: number;
-  /** Consist minus what bookings have claimed — what is still bookable. */
+  /** Capacity minus what bookings have claimed — what is still bookable. */
   wagonsRemaining: number;
 }
 
@@ -33,6 +33,8 @@ export function computeScheduleWagonUsage(input: {
   /** Stored counter; used only when the slot rows were not loaded. */
   storedWagonCount?: number | null;
   scheduleBookings?: ScheduleBookingLike[] | null;
+  /** Planned wagon ceiling (`maxWagons`) — what booking capacity is sold against. */
+  maxWagons?: number | null;
 }): ScheduleWagonUsage {
   const slots = input.wagonSlots ?? [];
 
@@ -42,7 +44,14 @@ export function computeScheduleWagonUsage(input: {
 
   // Prefer live slot rows; the stored counter drifts when a consist is edited
   // without a recompute, which is why the list and detail disagreed on totals.
-  const wagonsTotal = slots.length || (input.storedWagonCount ?? 0);
+  const coupled = slots.length || (input.storedWagonCount ?? 0);
+
+  // Wagons are coupled on demand as bookings are allocated, so a partially
+  // built consist does not cap what is bookable — the planned ceiling does
+  // (remainingWagonsForLeg sells against maxWagons). Without this, a schedule
+  // planned for 3 wagons with 2 coupled+allocated read "2/2 used, 0 bookable"
+  // while its detail page and the booking gate both said 1 wagon was free.
+  const wagonsTotal = Math.max(coupled, input.maxWagons ?? 0);
 
   // An unpaid booking still holds its wagons, so reserved space is NOT bookable.
   const wagonsReserved = (input.scheduleBookings ?? []).reduce(