test(ST-cmovhveh3): add pre-check integration tests for materializeIdeaPlanAction

Three new scenarios in ideas-crud.test.ts:
- auto-vervang: old PBI deleted in transaction when no executed tasks
- conflict-409: returns PBI_HAS_ACTIVE_TASKS:<code> with active tasks
- alongside: skips delete and creates new PBI when allowAlongside=true
Also adds task.count, pbi.findUnique, pbi.delete to prisma mock.

__tests__/actions/ideas-crud.test.ts

@@ -35,7 +35,9 @@ vi.mock('@/lib/prisma', () => ({
     pbi: {
       findFirst: vi.fn(),
       findMany: vi.fn(),
+      findUnique: vi.fn(),
       create: vi.fn(),
+      delete: vi.fn(),
     },
     story: {
       findMany: vi.fn(),
@@ -44,6 +46,7 @@ vi.mock('@/lib/prisma', () => ({
     task: {
       findMany: vi.fn(),
       create: vi.fn(),
+      count: vi.fn(),
     },
     $transaction: vi.fn(),
     $executeRaw: vi.fn().mockResolvedValue(0),
@@ -71,9 +74,9 @@ type MockIdea = {
   ideaLog: { create: ReturnType<typeof vi.fn> }
   claudeJob: { findFirst: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn>; update: ReturnType<typeof vi.fn> }
   claudeWorker: { count: ReturnType<typeof vi.fn> }
-  pbi: { findFirst: ReturnType<typeof vi.fn>; findMany: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn> }
+  pbi: { findFirst: ReturnType<typeof vi.fn>; findMany: ReturnType<typeof vi.fn>; findUnique: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn>; delete: ReturnType<typeof vi.fn> }
   story: { findMany: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn> }
-  task: { findMany: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn> }
+  task: { findMany: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn>; count: ReturnType<typeof vi.fn> }
   $transaction: ReturnType<typeof vi.fn>
   $executeRaw: ReturnType<typeof vi.fn>
 }
@@ -476,6 +479,69 @@ body
   })
 })
 
+describe('materializeIdeaPlanAction — existing PBI pre-check', () => {
+  const VALID_PLAN = `---
+pbi:
+  title: New PBI
+  priority: 2
+stories:
+  - title: Story A
+    priority: 2
+    tasks:
+      - title: Task A1
+        priority: 2
+---
+
+body
+`
+
+  beforeEach(() => {
+    // Use a distinct userId to avoid sharing the rate-limit bucket with the
+    // materializeIdeaPlanAction describe block above.
+    mockSession.userId = 'user-precheck'
+    m.idea.findFirst.mockResolvedValue({
+      id: 'idea-1',
+      status: 'PLAN_READY',
+      product_id: 'prod-1',
+      plan_md: VALID_PLAN,
+      pbi_id: 'old-pbi',
+    })
+    m.pbi.findMany.mockResolvedValue([])
+    m.story.findMany.mockResolvedValue([])
+    m.task.findMany.mockResolvedValue([])
+    m.pbi.findFirst.mockResolvedValue(null)
+    m.pbi.findUnique.mockResolvedValue({ code: 'PBI-X' })
+    m.pbi.create.mockResolvedValue({ id: 'pbi-new', code: 'PBI-2' })
+    m.pbi.delete.mockResolvedValue({})
+    m.story.create.mockResolvedValue({ id: 's-1' })
+    m.task.create.mockResolvedValue({ id: 't-1' })
+  })
+
+  it('auto-vervang: deletes old PBI in transaction when no tasks executed', async () => {
+    m.task.count.mockResolvedValueOnce(0)
+    const r = await materializeIdeaPlanAction('idea-1')
+    expect(r).toMatchObject({ success: true, data: { pbi_id: 'pbi-new' } })
+    expect(m.pbi.delete).toHaveBeenCalledWith({ where: { id: 'old-pbi' } })
+    expect(m.pbi.create).toHaveBeenCalledTimes(1)
+  })
+
+  it('conflict-409: returns PBI_HAS_ACTIVE_TASKS when executed tasks exist', async () => {
+    m.task.count.mockResolvedValueOnce(1)
+    const r = await materializeIdeaPlanAction('idea-1')
+    expect(r).toMatchObject({ code: 409, error: 'PBI_HAS_ACTIVE_TASKS:PBI-X' })
+    expect(m.pbi.create).not.toHaveBeenCalled()
+    expect(m.pbi.delete).not.toHaveBeenCalled()
+  })
+
+  it('alongside: skips old PBI delete and creates new PBI when allowAlongside=true', async () => {
+    m.task.count.mockResolvedValueOnce(1)
+    const r = await materializeIdeaPlanAction('idea-1', { allowAlongside: true })
+    expect(r).toMatchObject({ success: true, data: { pbi_id: 'pbi-new' } })
+    expect(m.pbi.delete).not.toHaveBeenCalled()
+    expect(m.pbi.create).toHaveBeenCalledTimes(1)
+  })
+})
+
 describe('relinkIdeaPlanAction', () => {
   it('happy: PLANNED with pbi_id=null → PLAN_READY', async () => {
     m.idea.findFirst.mockResolvedValueOnce({