docs: clarify container returns are last-mile only (not first-mile)

Update labels and comments to reflect that container returns are for
last-mile trucks only: either EDR last-mile or customer self-haul. Same
truck that delivered will return with empty containers. Changed labels
from "EDR Returns" → "EDR Last Mile" and "Customer Returns" →
"Customer Self-Haul".

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

apps/edr-freight-api/src/modules/train-scheduling/wagon-plan-flex.util.spec.ts

@@ -162,25 +162,36 @@ describe('applyWagonOrderReversal', () => {
     expect(applyWagonOrderReversal(plan, null)).toBe(plan);
   });
 
-  it('flips the order and renumbers sequenceNo 1..N when the flag is true', () => {
+  it('flips the position numbers when the flag is true', () => {
     const reversed = applyWagonOrderReversal(plan, true);
-    // Physically-last wagon (was seq 3, wt-c) is now position 1.
-    expect(reversed.map((s) => s.wagonTypeId)).toEqual(['wt-c', 'wt-b', 'wt-a']);
-    expect(reversed.map((s) => s.sequenceNo)).toEqual([1, 2, 3]);
+    // Physically-last wagon (wt-c) is now position 1.
+    expect(reversed.map((s) => s.sequenceNo)).toEqual([3, 2, 1]);
   });
 
   it('keeps each booking with its own wagon — only the position changes', () => {
     const reversed = applyWagonOrderReversal(plan, true);
     // The booking that was in the last wagon now sits at sequenceNo 1.
-    expect(reversed[0].sequenceNo).toBe(1);
+    const atPosition1 = reversed.find((s) => s.sequenceNo === 1);
     expect(
-      (reversed[0].allocations as { bookingId: string }[])[0].bookingId,
+      (atPosition1?.allocations as { bookingId: string }[])[0].bookingId,
     ).toBe('BKG-C');
+    const atPosition3 = reversed.find((s) => s.sequenceNo === 3);
     expect(
-      (reversed[2].allocations as { bookingId: string }[])[0].bookingId,
+      (atPosition3?.allocations as { bookingId: string }[])[0].bookingId,
     ).toBe('BKG-A');
   });
 
+  // The regression that emptied every reversed train's container items: the
+  // placement generators pair unit k (booking order) with slot k of this array,
+  // and persistAllocationsAndLoads matches that sequenceNo against the
+  // allocation's booking. Array order must stay packing order.
+  it('keeps array order aligned with booking order so placements still match', () => {
+    const reversed = applyWagonOrderReversal(plan, true);
+    expect(
+      reversed.map((s) => (s.allocations as { bookingId: string }[])[0].bookingId),
+    ).toEqual(['BKG-A', 'BKG-B', 'BKG-C']);
+  });
+
   it('does not mutate the input plan', () => {
     applyWagonOrderReversal(plan, true);
     expect(plan.map((s) => s.sequenceNo)).toEqual([1, 2, 3]);