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+---
+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 |
+| **Config file** | `ui/vitest.config.ts` (if exists) or created in Wave 0 |
+| **Quick run command** | `cd ui && pnpm test --run` |
+| **Full suite command** | `cd ui && pnpm test --run --coverage` |
+| **Estimated runtime** | ~15 seconds |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `cd ui && pnpm test --run`
+- **After every plan wave:** Run `cd ui && pnpm test --run --coverage`
+- **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 | CHAT-02, CHAT-03 | unit | `cd ui && pnpm test --run` | ❌ W0 | ⬜ pending |
+| 21-01-02 | 01 | 1 | HIST-01, HIST-02 | unit | `cd ui && pnpm test --run` | ❌ W0 | ⬜ pending |
+| 21-02-01 | 02 | 1 | CHAT-04, CHAT-05, CHAT-06 | unit | `cd ui && pnpm test --run` | ❌ W0 | ⬜ pending |
+| 21-02-02 | 02 | 1 | INPUT-01, INPUT-07 | unit | `cd ui && pnpm test --run` | ❌ W0 | ⬜ pending |
+| 21-03-01 | 03 | 2 | HIST-03, HIST-05, HIST-06 | unit | `cd ui && pnpm test --run` | ❌ W0 | ⬜ pending |
+| 21-03-02 | 03 | 2 | THEME-01, THEME-02 | visual | manual | N/A | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] `ui/src/__tests__/chat/` — test directory structure
+- [ ] Vitest config if not present
+- [ ] Test utilities for rendering with providers (theme, panel context)
+
+*Test stubs will be created during Wave 0 of execution if needed.*
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| Theme visual correctness | THEME-01, THEME-02 | Visual appearance cannot be tested with unit tests | Switch between Catppuccin Mocha, Tokyo Night, and Catppuccin Latte; verify code block highlighting matches active theme |
+| Markdown rendering fidelity | CHAT-04 | Complex rendering output hard to unit test fully | Send messages with code blocks, tables, lists, headings, links, inline images; verify each renders correctly |
+
+---
+
+## 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