feat(server): adopt zod DTOs for the assignment body contracts

shared/src/assignment/assignment.schema.spec.ts

@@ -2,6 +2,7 @@ import {
   assignmentCreateRequestSchema,
   assignmentMoveRequestSchema,
   assignmentParticipantsRequestSchema,
+  assignmentTransportRequestSchema,
 } from './assignment.schema';
 
 import { describe, it, expect } from 'vitest';
@@ -15,13 +16,24 @@ describe('assignmentCreateRequestSchema', () => {
 });
 
 describe('assignmentMoveRequestSchema', () => {
-  it('requires new_day_id; order_index optional', () => {
+  it('requires new_day_id; order_index optional/nullable', () => {
     expect(assignmentMoveRequestSchema.safeParse({ new_day_id: 4 }).success).toBe(true);
     expect(assignmentMoveRequestSchema.safeParse({ new_day_id: 4, order_index: 0 }).success).toBe(true);
+    // The client api sends `order_index: null` when no insert position is given.
+    expect(assignmentMoveRequestSchema.safeParse({ new_day_id: 4, order_index: null }).success).toBe(true);
     expect(assignmentMoveRequestSchema.safeParse({}).success).toBe(false);
   });
 });
 
+describe('assignmentTransportRequestSchema', () => {
+  it('accepts a mode, an explicit null, and an absent key (legacy `?? null`)', () => {
+    expect(assignmentTransportRequestSchema.safeParse({ transport_mode: 'cycling' }).success).toBe(true);
+    expect(assignmentTransportRequestSchema.safeParse({ transport_mode: null }).success).toBe(true);
+    expect(assignmentTransportRequestSchema.safeParse({}).success).toBe(true);
+    expect(assignmentTransportRequestSchema.safeParse({ transport_mode: 5 }).success).toBe(false);
+  });
+});
+
 describe('assignmentParticipantsRequestSchema', () => {
   it('requires a numeric user_ids array', () => {
     expect(assignmentParticipantsRequestSchema.safeParse({ user_ids: [1, 2] }).success).toBe(true);

shared/src/assignment/assignment.schema.ts

@@ -7,10 +7,11 @@ import { z } from 'zod';
  * endpoints under /api/trips/:tripId/days/:dayId/assignments and
  * /api/trips/:tripId/assignments/:id/*.
  *
- * Trip-scoped; mutations use the 'day_edit' permission. The legacy route
- * (server/src/routes/assignments.ts, mounted on /api) wraps assignmentService.
- * Assignment rows carry joined place data and are kept open in responses; the
- * request schemas + the bespoke 404/400 controller messages pin the rest.
+ * Trip-scoped; mutations use the 'day_edit' permission. The server side is the
+ * DI-native AssignmentsService (server/src/nest/assignments/), validated via
+ * the createZodDto wrappers in assignments.dto.ts. Assignment rows carry
+ * joined place data and are kept open in responses; the request schemas + the
+ * bespoke 404 controller messages pin the rest.
  */
 
 /**
@@ -61,7 +62,9 @@ export type AssignmentReorderRequest = z.infer<typeof assignmentReorderRequestSc
 
 export const assignmentMoveRequestSchema = z.object({
   new_day_id: z.union([z.number(), z.string()]),
-  order_index: z.number().optional(),
+  // The client api types this `number | null` (assignmentsApi.move) and the
+  // legacy route accepted null (`orderIndex || 0`) — keep null on the wire.
+  order_index: z.number().nullable().optional(),
 });
 export type AssignmentMoveRequest = z.infer<typeof assignmentMoveRequestSchema>;
 
@@ -73,7 +76,9 @@ export type AssignmentTimeRequest = z.infer<typeof assignmentTimeRequestSchema>;
 
 /** Set the leg's travel mode (a RouteProfileKey, or null to inherit the day default). */
 export const assignmentTransportRequestSchema = z.object({
-  transport_mode: z.string().nullable(),
+  // The legacy route read `body.transport_mode ?? null`, so an absent key
+  // behaves like an explicit null — keep it optional on the wire.
+  transport_mode: z.string().nullable().optional(),
 });
 export type AssignmentTransportRequest = z.infer<typeof assignmentTransportRequestSchema>;