docs(phase-26): add validation strategy and research

.planning/phases/26-pwa-performance/26-VALIDATION.md

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+---
+phase: 26
+slug: pwa-performance
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: 2026-04-02
+---
+
+# Phase 26 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | vitest 3.x |
+| **Config file** | vitest.config.ts (existing) |
+| **Quick run command** | `npx vitest run --no-coverage` |
+| **Full suite command** | `npx vitest run --no-coverage` |
+| **Estimated runtime** | ~5 seconds |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `npx vitest run --no-coverage`
+- **After every plan wave:** Run `npx vitest run --no-coverage`
+- **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 |
+|---------|------|------|-------------|-----------|-------------------|-------------|--------|
+| TBD | TBD | TBD | PWA-01..08, PERF-01, PERF-05 | unit+integration | `npx vitest run` | TBD | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+*Note: Task-level mapping will be populated by the planner.*
+
+---
+
+## Wave 0 Requirements
+
+- Existing vitest infrastructure covers server and UI tests
+- No new test framework installation needed
+
+*Existing infrastructure covers all phase requirements.*
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| Add to Home Screen prompt | PWA-01 | Browser-specific install prompt | Visit on mobile Chrome, verify install banner |
+| Splash screen and icon | PWA-02 | Visual rendering on device | Install PWA, verify icon and splash |
+| Offline mode + message queue | PWA-03, PWA-04 | Requires network disconnection | Disable network, verify cached UI loads, send message, reconnect |
+| Mobile keyboard layout | PWA-05 | Physical device interaction | Open on phone, verify sticky input bar with keyboard |
+| Pull-to-refresh gesture | PWA-06 | Touch gesture on mobile | Pull down on conversation list |
+| Push notifications | PWA-07 | Requires real push subscription | Accept notifications, trigger agent event |
+| Page load time | PERF-01, PERF-05 | Requires Lighthouse/DevTools | Run Lighthouse audit, verify <2s broadband |
+
+---
+
+## 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