feat(train-scheduling): log leg-slot board/alight events at checkpoints

Leg slots (stampSlotLegs — bookings boarding/alighting mid-corridor)
reaching their board/alight yard produced no ScheduleWagonAdjustmentLog
row, unlike planned couples/cuts. Without it the marshalling document
has no way to show a wagon coupling in already loaded, or uncoupling
with cargo, at a mid-corridor stop.

recordCheckpoint now logs ADD at the board yard and REMOVE at the
alight yard for these slots, deduped against existing rows since
passedYardIds re-includes earlier stops on every checkpoint call.
Purely observational — the physical wagon was already pinned to the
slot at schedule-build time, so no wagon/consist state changes.

Stage 3 of the multi-stop marshalling plan (per-event numbered docs);
stages 4-6 (generalized doc builder, endpoints, UI) still open.

apps/edr-freight-api/src/modules/train-scheduling/services/train-scheduling.service.ts

@@ -5007,6 +5007,76 @@ export class TrainSchedulingService {
             await manager.getRepository(ScheduleWagonAdjustmentLog).save(coupleLogRows);
           }
         }
+
+        // Leg slots (booking legs boarding/alighting mid-corridor — see
+        // stampSlotLegs) reaching their board/alight yard here: logged same as
+        // planned couples/cuts above, so the marshalling document can show
+        // what coupled ALREADY LOADED / uncoupled WITH cargo at this stop.
+        // Purely observational — their physical wagon was already pinned to
+        // the slot at schedule-build time (assignPhysicalWagonsToSlots), so
+        // nothing here changes wagon state, only the log. Dedupe against
+        // existing rows (not a wagon-state flag, unlike the couple/cut blocks
+        // above) since passedYardIds re-includes earlier stops on every call.
+        const legSlotsHere = (schedule.trainSet?.wagons ?? []).filter(
+          (slot) =>
+            slot.physicalWagonId &&
+            ((slot.boardYardId && passedYardIds.includes(slot.boardYardId)) ||
+              (slot.alightYardId && passedYardIds.includes(slot.alightYardId))),
+        );
+        if (legSlotsHere.length && builtTrainId) {
+          const legWagonIds = [
+            ...new Set(legSlotsHere.map((slot) => slot.physicalWagonId!)),
+          ];
+          const legWagonById = new Map(
+            (
+              await manager.getRepository(Wagon).find({ where: { id: In(legWagonIds) } })
+            ).map((w) => [w.id, w]),
+          );
+          const alreadyLogged = new Set(
+            (
+              await manager.getRepository(ScheduleWagonAdjustmentLog).find({
+                where: {
+                  trainScheduleId: scheduleId,
+                  wagonId: In(legWagonIds),
+                  action: In(['ADD', 'REMOVE']),
+                },
+              })
+            ).map((row) => `${row.wagonId}:${row.action}:${row.yardId}`),
+          );
+          const legLogRows: ScheduleWagonAdjustmentLog[] = [];
+          for (const slot of legSlotsHere) {
+            const wagon = legWagonById.get(slot.physicalWagonId!);
+            if (!wagon) continue;
+            const events: Array<{ action: 'ADD' | 'REMOVE'; yardId: string }> = [];
+            if (slot.boardYardId && passedYardIds.includes(slot.boardYardId)) {
+              events.push({ action: 'ADD', yardId: slot.boardYardId });
+            }
+            if (slot.alightYardId && passedYardIds.includes(slot.alightYardId)) {
+              events.push({ action: 'REMOVE', yardId: slot.alightYardId });
+            }
+            for (const { action, yardId } of events) {
+              const key = `${wagon.id}:${action}:${yardId}`;
+              if (alreadyLogged.has(key)) continue;
+              alreadyLogged.add(key);
+              legLogRows.push(
+                manager.getRepository(ScheduleWagonAdjustmentLog).create({
+                  trainScheduleId: scheduleId,
+                  trainId: builtTrainId,
+                  action,
+                  wagonId: wagon.id,
+                  wagonNumber: wagon.wagonNumber,
+                  adjustedByUserId: null,
+                  yardId,
+                  occurredAt,
+                }),
+              );
+            }
+          }
+          if (legLogRows.length) {
+            await manager.getRepository(ScheduleWagonAdjustmentLog).save(legLogRows);
+          }
+        }
+
         await manager
           .getRepository(Wagon)
           .createQueryBuilder()