brain/gateway: prohibit mission_tasks.status as a write source (M4-3a phase 1)

SHARED-CONTRACT §5.1 phase 1 N-1 patch, ahead of the M4-3a expand DDL:
- mission-tasks repo (sole write path) strips status on create/update;
  the column keeps its DB default and stays declared and readable.
- missions controller stops forwarding dto.status on create.
- DTO status fields stay declared (forbidNonWhitelisted would 400 frozen
  legacy consumers) but are documented deprecated/ignored.
- §5.5 write-prohibition spec: 4 tests on what reaches the Drizzle chain.

packages/brain/src/mission-tasks.spec.ts

@@ -0,0 +1,77 @@
+import { describe, it, expect, vi } from 'vitest';
+import { createMissionTasksRepo } from './mission-tasks.js';
+
+/**
+ * SHARED-CONTRACT §5.5 "mission_tasks.status write prohibition": the repo is
+ * the sole write path, and it must never forward a caller-supplied status to
+ * the database on create or update. Callers keep working (the field is
+ * accepted and ignored), so these tests assert on what reaches the Drizzle
+ * chain, not on rejection.
+ */
+
+function makeInsertDb(returned: unknown[]) {
+  const values = vi.fn((_v: unknown) => ({ returning: vi.fn().mockResolvedValue(returned) }));
+  return { db: { insert: vi.fn(() => ({ values })) }, values };
+}
+
+function makeUpdateDb(returned: unknown[]) {
+  const set = vi.fn((_v: unknown) => ({
+    where: vi.fn(() => ({ returning: vi.fn().mockResolvedValue(returned) })),
+  }));
+  return { db: { update: vi.fn(() => ({ set })) }, set };
+}
+
+describe('createMissionTasksRepo — status write prohibition', () => {
+  it('create strips a caller-supplied status before insert', async () => {
+    const { db, values } = makeInsertDb([{ id: 'mt1', status: 'not-started' }]);
+    const repo = createMissionTasksRepo(db as never);
+
+    const result = await repo.create({
+      missionId: 'm1',
+      userId: 'u1',
+      status: 'done',
+      description: 'd',
+    } as never);
+
+    expect(values).toHaveBeenCalledTimes(1);
+    const inserted = values.mock.calls[0]![0] as Record<string, unknown>;
+    expect('status' in inserted).toBe(false);
+    expect(inserted.missionId).toBe('m1');
+    expect(inserted.description).toBe('d');
+    expect(result.id).toBe('mt1');
+  });
+
+  it('create without status still inserts (DB default applies)', async () => {
+    const { db, values } = makeInsertDb([{ id: 'mt2' }]);
+    const repo = createMissionTasksRepo(db as never);
+
+    await repo.create({ missionId: 'm1', userId: 'u1' } as never);
+
+    const inserted = values.mock.calls[0]![0] as Record<string, unknown>;
+    expect('status' in inserted).toBe(false);
+  });
+
+  it('update strips a caller-supplied status but keeps the other fields', async () => {
+    const { db, set } = makeUpdateDb([{ id: 'mt1', notes: 'n' }]);
+    const repo = createMissionTasksRepo(db as never);
+
+    const result = await repo.update('mt1', { status: 'done', notes: 'n' } as never);
+
+    expect(set).toHaveBeenCalledTimes(1);
+    const updated = set.mock.calls[0]![0] as Record<string, unknown>;
+    expect('status' in updated).toBe(false);
+    expect(updated.notes).toBe('n');
+    expect(updated.updatedAt).toBeInstanceOf(Date);
+    expect(result?.id).toBe('mt1');
+  });
+
+  it('update with only status degenerates to a timestamp-only update', async () => {
+    const { db, set } = makeUpdateDb([{ id: 'mt1' }]);
+    const repo = createMissionTasksRepo(db as never);
+
+    await repo.update('mt1', { status: 'blocked' } as never);
+
+    const updated = set.mock.calls[0]![0] as Record<string, unknown>;
+    expect(Object.keys(updated)).toEqual(['updatedAt']);
+  });
+});

packages/brain/src/mission-tasks.ts

@@ -3,6 +3,18 @@ import { eq, and, type Db, missionTasks } from '@mosaicstack/db';
 export type MissionTask = typeof missionTasks.$inferSelect;
 export type NewMissionTask = typeof missionTasks.$inferInsert;
 
+// SHARED-CONTRACT §5.1 phase 1 / §5.4: mission_tasks.status is prohibited as a
+// write source through the N-1 window. This repo is the sole write path, so the
+// field is stripped here — accepted and ignored rather than rejected, because
+// the legacy surface is frozen with existing consumers kept working
+// (tool-gateway-mapping.md §3.2). The column keeps its DB default, stays
+// declared and readable, and is retired only after no readers remain.
+function stripStatus<T extends { status?: unknown }>(data: T): Omit<T, 'status'> {
+  const rest = { ...data };
+  delete rest.status;
+  return rest;
+}
+
 export function createMissionTasksRepo(db: Db) {
   return {
     async findByMission(missionId: string): Promise<MissionTask[]> {
@@ -30,14 +42,14 @@ export function createMissionTasksRepo(db: Db) {
     },
 
     async create(data: NewMissionTask): Promise<MissionTask> {
-      const rows = await db.insert(missionTasks).values(data).returning();
+      const rows = await db.insert(missionTasks).values(stripStatus(data)).returning();
       return rows[0]!;
     },
 
     async update(id: string, data: Partial<NewMissionTask>): Promise<MissionTask | undefined> {
       const rows = await db
         .update(missionTasks)
-        .set({ ...data, updatedAt: new Date() })
+        .set({ ...stripStatus(data), updatedAt: new Date() })
         .where(eq(missionTasks.id, id))
         .returning();
       return rows[0];