feat(ST-1112): wire story-promotion into saveTask and PATCH /api/tasks/:id

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

__tests__/api/tasks.test.ts

@@ -5,7 +5,13 @@ vi.mock('@/lib/prisma', () => ({
     task: {
       findFirst: vi.fn(),
       update: vi.fn(),
+      findMany: vi.fn(),
     },
+    story: {
+      findUniqueOrThrow: vi.fn(),
+      update: vi.fn(),
+    },
+    $transaction: vi.fn(),
   },
 }))
 
@@ -18,7 +24,16 @@ import { authenticateApiRequest } from '@/lib/api-auth'
 import { PATCH as patchTask } from '@/app/api/tasks/[id]/route'
 
 const mockPrisma = prisma as unknown as {
-  task: { findFirst: ReturnType<typeof vi.fn>; update: ReturnType<typeof vi.fn> }
+  task: {
+    findFirst: ReturnType<typeof vi.fn>
+    update: ReturnType<typeof vi.fn>
+    findMany: ReturnType<typeof vi.fn>
+  }
+  story: {
+    findUniqueOrThrow: ReturnType<typeof vi.fn>
+    update: ReturnType<typeof vi.fn>
+  }
+  $transaction: ReturnType<typeof vi.fn>
 }
 const mockAuth = authenticateApiRequest as ReturnType<typeof vi.fn>
 
@@ -55,6 +70,15 @@ describe('PATCH /api/tasks/:id', () => {
       id: 'task-1',
       status: 'DONE',
       implementation_plan: null,
+      title: 'Task',
+      story_id: 'story-1',
+    })
+    // Default sibling state: only this task, already DONE → no story-promotion
+    mockPrisma.task.findMany.mockResolvedValue([{ status: 'DONE' }])
+    mockPrisma.story.findUniqueOrThrow.mockResolvedValue({ status: 'DONE' })
+    // Pass-through for $transaction so tests behave as if Prisma ran the run-fn directly.
+    mockPrisma.$transaction.mockImplementation(async (run: (tx: typeof prisma) => Promise<unknown>) => {
+      return run(prisma)
     })
   })
 
@@ -111,17 +135,28 @@ describe('PATCH /api/tasks/:id', () => {
   // TC-T-10
   it('updates both status and implementation_plan and returns 200', async () => {
     const plan = 'Full plan here.'
-    mockPrisma.task.update.mockResolvedValue({ id: 'task-1', status: 'DONE', implementation_plan: plan })
+    // First update writes the implementation_plan; second is the helper's status write.
+    mockPrisma.task.update
+      .mockResolvedValueOnce({ id: 'task-1', status: 'TO_DO', implementation_plan: plan })
+      .mockResolvedValueOnce({
+        id: 'task-1',
+        title: 'Task',
+        status: 'DONE',
+        story_id: 'story-1',
+        implementation_plan: plan,
+      })
 
     const res = await patchTask(...makeRequest({ status: 'done', implementation_plan: plan }))
     const data = await res.json()
 
     expect(res.status).toBe(200)
     expect(data).toMatchObject({ status: 'done', implementation_plan: plan })
+    // implementation_plan written via direct update; status written via helper update.
     expect(mockPrisma.task.update).toHaveBeenCalledWith(
-      expect.objectContaining({
-        data: { status: 'DONE', implementation_plan: plan },
-      })
+      expect.objectContaining({ data: { implementation_plan: plan } }),
+    )
+    expect(mockPrisma.task.update).toHaveBeenCalledWith(
+      expect.objectContaining({ data: { status: 'DONE' } }),
     )
   })
 
@@ -146,6 +181,25 @@ describe('PATCH /api/tasks/:id', () => {
     expect(reviewRes.status).toBe(422)
   })
 
+  it('promotes story to DONE when last sibling task transitions to DONE', async () => {
+    mockPrisma.task.update.mockResolvedValue({
+      id: 'task-1',
+      status: 'DONE',
+      implementation_plan: null,
+      title: 'Task',
+      story_id: 'story-1',
+    })
+    mockPrisma.task.findMany.mockResolvedValue([{ status: 'DONE' }, { status: 'DONE' }])
+    mockPrisma.story.findUniqueOrThrow.mockResolvedValue({ status: 'IN_SPRINT' })
+
+    const res = await patchTask(...makeRequest({ status: 'done' }))
+    expect(res.status).toBe(200)
+    expect(mockPrisma.story.update).toHaveBeenCalledWith({
+      where: { id: 'story-1' },
+      data: { status: 'DONE' },
+    })
+  })
+
   it('returns 400 for malformed JSON', async () => {
     const req = new Request('http://localhost/api/tasks/task-1', {
       method: 'PATCH',