add wagon allocation snapshot to train schedules

apps/edr-freight-api/src/modules/train-schedules/entities/train-schedule.entity.ts

@@ -1,5 +1,8 @@
 import { BaseEntity } from '@edr/api-common';
-import { TrainScheduleStatus as TrainScheduleStatusEnum } from '@edr/types';
+import {
+  TrainScheduleStatus as TrainScheduleStatusEnum,
+  WagonAllocationSnapshot,
+} from '@edr/types';
 import { Column, Entity, Index, JoinColumn, ManyToOne, OneToMany, OneToOne } from 'typeorm';
 
 import { Yard } from '../../rule-engine/entities/yard.entity';
@@ -146,6 +149,14 @@ export class TrainSchedule extends BaseEntity {
   @Column({ name: 'rule_export_booking_lead_hours', type: 'int', nullable: true })
   ruleExportBookingLeadHours?: number | null;
 
+  // Frozen wagon plan captured once when the schedule leaves the editable
+  // DRAFT/SCHEDULED phase (dispatch / arrive / cancel). Admin views of a
+  // non-editable schedule read THIS instead of the live wagon↔slot joins, so the
+  // historical allocation survives the same physical wagons being re-pinned onto
+  // later trains. NULL while DRAFT/SCHEDULED (read live) and on legacy rows.
+  @Column({ name: 'wagon_allocation_snapshot', type: 'jsonb', nullable: true })
+  wagonAllocationSnapshot?: WagonAllocationSnapshot | null;
+
   @OneToMany(() => TrainScheduleBooking, (scheduleBooking) => scheduleBooking.trainSchedule)
   scheduleBookings?: TrainScheduleBooking[];
 }