lib: idea-code generator + plan_md yaml-frontmatter parser (M12 T-494)

- lib/idea-code.ts: pure formatIdeaCode helper (client-safe, no prisma)
- lib/idea-code-server.ts: atomic nextIdeaCode via Prisma row-lock,
  accepts optional TransactionClient for combining with idea.create
- lib/idea-plan-parser.ts: parsePlanMd extracts ---yaml---/body, runs
  yaml.parse + ideaPlanMdFrontmatterSchema, returns line-info on failure;
  CRLF-tolerant
- adds yaml@^2.8.4 dependency
- 8 unit tests (parser happy/missing/yaml-error/zod-error/empty-stories/CRLF;
  formatIdeaCode pad-3 + overflow)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

__tests__/lib/idea-code.test.ts

@@ -0,0 +1,21 @@
+import { describe, it, expect } from 'vitest'
+
+import { formatIdeaCode } from '@/lib/idea-code'
+
+describe('formatIdeaCode', () => {
+  it('pads to 3 digits', () => {
+    expect(formatIdeaCode(1)).toBe('IDEA-001')
+    expect(formatIdeaCode(42)).toBe('IDEA-042')
+    expect(formatIdeaCode(999)).toBe('IDEA-999')
+  })
+
+  it('does not truncate beyond pad-width', () => {
+    expect(formatIdeaCode(1000)).toBe('IDEA-1000')
+    expect(formatIdeaCode(99999)).toBe('IDEA-99999')
+  })
+})
+
+// Integration-style concurrency-test op nextIdeaCode is in
+// __tests__/integration/ tests die de echte DB raken (zie M12 verificatie-stap).
+// Hier alleen de pure formatter; de increment-logica leunt op Prisma's
+// row-lock in $transaction die we per-database vertrouwen.

__tests__/lib/idea-plan-parser.test.ts

@@ -0,0 +1,103 @@
+import { describe, it, expect } from 'vitest'
+
+import { parsePlanMd } from '@/lib/idea-plan-parser'
+
+const VALID = `---
+pbi:
+  title: Test PBI
+  priority: 2
+stories:
+  - title: Eerste flow
+    priority: 2
+    tasks:
+      - title: Setup
+        priority: 2
+        implementation_plan: |
+          1. Doe X
+          2. Doe Y
+---
+
+# Overwegingen
+
+Dit is de body, niet geparsed.
+`
+
+describe('parsePlanMd', () => {
+  it('parses a valid plan', () => {
+    const r = parsePlanMd(VALID)
+    expect(r.ok).toBe(true)
+    if (r.ok) {
+      expect(r.plan.pbi.title).toBe('Test PBI')
+      expect(r.plan.stories).toHaveLength(1)
+      expect(r.plan.stories[0].tasks).toHaveLength(1)
+      expect(r.plan.stories[0].tasks[0].implementation_plan).toContain('Doe X')
+      expect(r.body).toContain('# Overwegingen')
+    }
+  })
+
+  it('rejects when frontmatter is missing', () => {
+    const r = parsePlanMd('# Just markdown\n\nNo frontmatter here.')
+    expect(r.ok).toBe(false)
+    if (!r.ok) {
+      expect(r.errors[0].line).toBe(1)
+      expect(r.errors[0].message).toMatch(/frontmatter/i)
+    }
+  })
+
+  it('reports yaml syntax error with line info', () => {
+    const broken = `---
+pbi:
+  title: Test
+  priority: [unclosed
+stories:
+  - foo
+---
+
+body
+`
+    const r = parsePlanMd(broken)
+    expect(r.ok).toBe(false)
+    if (!r.ok) {
+      expect(r.errors[0].message.length).toBeGreaterThan(0)
+    }
+  })
+
+  it('reports schema-validation error when pbi-section missing', () => {
+    const noPbi = `---
+stories:
+  - title: x
+    priority: 2
+    tasks:
+      - title: y
+        priority: 2
+---
+
+body
+`
+    const r = parsePlanMd(noPbi)
+    expect(r.ok).toBe(false)
+    if (!r.ok) {
+      expect(r.errors.some((e) => e.message.includes('pbi'))).toBe(true)
+    }
+  })
+
+  it('rejects empty stories array', () => {
+    const noStories = `---
+pbi:
+  title: x
+  priority: 2
+stories: []
+---
+
+body
+`
+    const r = parsePlanMd(noStories)
+    expect(r.ok).toBe(false)
+  })
+
+  it('handles CRLF line endings', () => {
+    const crlf = VALID.replace(/\n/g, '\r\n')
+    const r = parsePlanMd(crlf)
+    expect(r.ok).toBe(true)
+  })
+})