docs(phase-8): add validation strategy

.planning/phases/08-theme-foundation/08-VALIDATION.md

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+---
+phase: 8
+slug: theme-foundation
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: 2026-03-31
+---
+
+# Phase 8 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | Vitest ^4.1.1 |
+| **Config file** | `vite.config.ts` (test block: `environment: 'jsdom'`) |
+| **Quick run command** | `npm test` |
+| **Full suite command** | `npm test` |
+| **Estimated runtime** | ~5 seconds |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `npm test`
+- **After every plan wave:** Run `npm test`
+- **Before `/gsd:verify-work`:** Full suite must be green
+- **Max feedback latency:** 10 seconds
+
+---
+
+## Per-Task Verification Map
+
+| Task ID | Plan | Wave | Requirement | Test Type | Automated Command | File Exists | Status |
+|---------|------|------|-------------|-----------|-------------------|-------------|--------|
+| 08-01-01 | 01 | 0 | THEME-02 | unit | `npm test` | ❌ W0 | ⬜ pending |
+| 08-02-01 | 02 | 1 | THEME-01 | unit | `npm test` | ✅ existing | ⬜ pending |
+| 08-02-02 | 02 | 1 | THEME-01 | grep | `grep -r "text-gray-\|bg-gray-\|border-gray-\|bg-blue-\|text-blue-" src/` | manual | ⬜ pending |
+| 08-03-01 | 03 | 1 | THEME-02 | unit | `npm test` | ❌ W0 | ⬜ pending |
+| 08-03-02 | 03 | 1 | THEME-02 | manual | Browser: dark OS → hard reload → no flash | manual-only | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] `src/components/ui/ThemeToggle.test.tsx` — stubs for THEME-02 (toggle render, dark class toggle, localStorage persistence)
+
+*Existing 5 test files use semantic queries (getByText, getByRole) — unaffected by class-name migration.*
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| No flash of wrong theme on reload | THEME-02 | Requires browser paint timing — jsdom cannot verify visual flash | 1. Set theme to Dark, reload page 2. Set theme to Light, reload in dark OS mode 3. Clear localStorage, reload — should follow OS preference |
+
+---
+
+## 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 < 10s
+- [ ] `nyquist_compliant: true` set in frontmatter
+
+**Approval:** pending