docs(phase-16): add validation strategy

.planning/phases/16-multi-user-data-model/16-VALIDATION.md

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+---
+phase: 16
+slug: multi-user-data-model
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: 2026-04-05
+---
+
+# Phase 16 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | Bun test runner (built-in) |
+| **Config file** | none (Bun built-in) |
+| **Quick run command** | `bun test tests/services/item.service.test.ts` |
+| **Full suite command** | `bun test` |
+| **Estimated runtime** | ~30 seconds (individual files) |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `bun test` (affected file)
+- **After every plan wave:** Run `bun test` (full suite)
+- **Before `/gsd:verify-work`:** Full suite must be green
+- **Max feedback latency:** 30 seconds
+
+---
+
+## Per-Task Verification Map
+
+| Task ID | Plan | Wave | Requirement | Test Type | Automated Command | File Exists | Status |
+|---------|------|------|-------------|-----------|-------------------|-------------|--------|
+| 16-01-01 | 01 | 1 | MULTI-01 | unit | `bun test tests/services/item.service.test.ts` | ✅ (needs update) | ⬜ pending |
+| 16-01-02 | 01 | 1 | MULTI-03 | unit | `bun test tests/services/category.service.test.ts` | ✅ (needs update) | ⬜ pending |
+| 16-02-01 | 02 | 2 | MULTI-02 | unit | `bun test tests/services/item.service.test.ts` | ❌ W0 (new isolation test) | ⬜ pending |
+| 16-02-02 | 02 | 2 | MULTI-05 | unit | `bun test tests/mcp/tools.test.ts` | ✅ (needs update) | ⬜ pending |
+| 16-02-03 | 02 | 2 | MULTI-06 | unit | `bun test tests/routes/settings.test.ts` | ✅ (needs update) | ⬜ pending |
+| 16-03-01 | 03 | 3 | MULTI-04 | integration | Migration verification | ❌ W0 | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] Update `createTestDb()` to return `{ db, userId }` with seeded user
+- [ ] Add cross-user isolation tests (create as user A, verify user B can't see)
+- [ ] Update all service tests to pass userId parameter
+- [ ] Update all route tests to set userId in context
+- [ ] Update MCP tool tests to pass userId
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| Existing data migrated to first user | MULTI-04 | Requires real migration against existing DB | Run migration on dev DB, verify all items/categories/threads/setups have userId = 1 |
+
+---
+
+## Validation Sign-Off
+
+- [ ] All tasks have `<automated>` verify or Wave 0 dependencies
+- [ ] Sampling continuity: no 3 consecutive tasks without automated verify
+- [ ] Wave 0 covers all MISSING references
+- [ ] No watch-mode flags
+- [ ] Feedback latency < 30s
+- [ ] `nyquist_compliant: true` set in frontmatter
+
+**Approval:** pending