[nexus] docs(21): add validation strategy

.planning/phases/21-chat-foundation/21-VALIDATION.md

@@ -0,0 +1,82 @@
+---
+phase: 21
+slug: chat-foundation
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: 2026-04-01
+---
+
+# Phase 21 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | Vitest 3.x |
+| **Config file** | `server/vitest.config.ts` (server), `vitest.config.ts` (root, multi-project) |
+| **Quick run command** | `pnpm vitest run server/src/__tests__/chat-service.test.ts` |
+| **Full suite command** | `pnpm test:run` |
+| **Estimated runtime** | ~15 seconds |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `pnpm vitest run server/src/__tests__/chat-service.test.ts`
+- **After every plan wave:** Run `pnpm test:run`
+- **Before `/gsd:verify-work`:** Full suite must be green
+- **Max feedback latency:** 15 seconds
+
+---
+
+## Per-Task Verification Map
+
+| Task ID | Plan | Wave | Requirement | Test Type | Automated Command | File Exists | Status |
+|---------|------|------|-------------|-----------|-------------------|-------------|--------|
+| 21-01-01 | 01 | 1 | HIST-01 | unit (service) | `pnpm vitest run server/src/__tests__/chat-service.test.ts` | ❌ W0 | ⬜ pending |
+| 21-01-02 | 01 | 1 | HIST-01 | integration (route) | `pnpm vitest run server/src/__tests__/chat-routes.test.ts` | ❌ W0 | ⬜ pending |
+| 21-01-03 | 01 | 1 | CHAT-04 | unit (service) | `pnpm vitest run server/src/__tests__/chat-service.test.ts` | ❌ W0 | ⬜ pending |
+| 21-01-04 | 01 | 1 | CHAT-05 | unit (service) | `pnpm vitest run server/src/__tests__/chat-service.test.ts` | ❌ W0 | ⬜ pending |
+| 21-01-05 | 01 | 1 | CHAT-06 | unit (service) | `pnpm vitest run server/src/__tests__/chat-service.test.ts` | ❌ W0 | ⬜ pending |
+| 21-02-01 | 02 | 1 | CHAT-02, CHAT-03 | component (UI) | `pnpm vitest run ui/src/components/ChatMarkdownMessage.test.tsx` | ❌ W0 | ⬜ pending |
+| 21-02-02 | 02 | 1 | INPUT-07 | component (UI) | `pnpm vitest run ui/src/components/ChatInput.test.tsx` | ❌ W0 | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] `server/src/__tests__/chat-service.test.ts` — stubs for HIST-01, CHAT-04, CHAT-05, CHAT-06
+- [ ] `server/src/__tests__/chat-routes.test.ts` — stubs for HIST-01 route integration
+- [ ] `ui/src/components/ChatMarkdownMessage.test.tsx` — stubs for CHAT-02, CHAT-03
+- [ ] `ui/src/components/ChatInput.test.tsx` — stubs for INPUT-07
+
+*Existing vitest infrastructure covers framework install.*
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| Theme CSS variables apply to chat panel and code blocks | THEME-01, THEME-02 | Visual inspection required | Open app, switch themes (Catppuccin Mocha, Tokyo Night, Catppuccin Latte), verify chat panel and code block colors match theme |
+| Infinite scroll loads next page on scroll to bottom | HIST-03 | Requires browser scroll simulation | Create 50+ messages, scroll to bottom, verify next page loads |
+
+---
+
+## 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 < 15s
+- [ ] `nyquist_compliant: true` set in frontmatter
+
+**Approval:** pending