back date validator

apps/edr-freight-api/src/modules/train-scheduling/dto/record-checkpoint.dto.ts

@@ -10,6 +10,8 @@ import {
   Min,
 } from 'class-validator';
 
+import { IsNotBackdated } from '../../../common/validators/is-not-backdated.validator';
+
 export class RecordCheckpointDto {
   @ApiProperty({ description: 'Station position along the route (0 = origin).' })
   @IsInt()
@@ -21,9 +23,18 @@ export class RecordCheckpointDto {
   @IsEnum(TrainCheckpointKind)
   kind?: TrainCheckpointKind;
 
-  @ApiProperty({ required: false, description: 'ISO timestamp; defaults to now.' })
+  /**
+   * A checkpoint records where the train is as staff observe it, and the final
+   * one arrives the schedule — so a backdated value rewrites the journey after
+   * the fact. Only "now" is accepted; omit the field and the service stamps it.
+   */
+  @ApiProperty({
+    required: false,
+    description: 'ISO timestamp; defaults to now. Cannot be earlier than now.',
+  })
   @IsOptional()
   @IsISO8601()
+  @IsNotBackdated()
   occurredAt?: string;
 
   @ApiProperty({ required: false })