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+---
+phase: 4
+slug: chart-polish-and-bug-fixes
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: 2026-03-12
+---
+
+# Phase 4 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | Vitest (configured in `vite.config.ts`) |
+| **Config file** | `frontend/vite.config.ts` — `test` block with `environment: 'jsdom'`, `setupFiles: ['./src/test-setup.ts']` |
+| **Quick run command** | `cd frontend && bun vitest run src/lib/format.test.ts` |
+| **Full suite command** | `cd frontend && bun vitest run` |
+| **Estimated runtime** | ~5 seconds |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** Run `cd frontend && bun vitest run src/lib/format.test.ts`
+- **After every plan wave:** Run `cd frontend && bun vitest run`
+- **Before `/gsd:verify-work`:** Full suite must be green
+- **Max feedback latency:** 5 seconds
+
+---
+
+## Per-Task Verification Map
+
+| Task ID | Plan | Wave | Requirement | Test Type | Automated Command | File Exists | Status |
+|---------|------|------|-------------|-----------|-------------------|-------------|--------|
+| 04-01-01 | 01 | 1 | FIX-01 | unit | `cd frontend && bun vitest run src/lib/format.test.ts` | ❌ W0 | ⬜ pending |
+| 04-01-02 | 01 | 1 | FIX-01 | unit | `cd frontend && bun vitest run src/lib/format.test.ts` | ❌ W0 | ⬜ pending |
+| 04-02-01 | 02 | 1 | IXTN-04 | unit | `cd frontend && bun vitest run src/components/ExpenseBreakdown.test.tsx` | ❌ W0 | ⬜ pending |
+| 04-02-02 | 02 | 1 | IXTN-04 | unit | `cd frontend && bun vitest run src/components/AvailableBalance.test.tsx` | ❌ W0 | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] `frontend/src/lib/format.test.ts` — unit tests for FIX-01 locale parameter and default behavior
+- [ ] `frontend/src/components/ExpenseBreakdown.test.tsx` — IXTN-04 tooltip formatter unit tests
+- [ ] `frontend/src/components/AvailableBalance.test.tsx` — IXTN-04 tooltip formatter unit tests on donut
+
+*Note: Recharts tooltip tests should test the formatter function directly rather than simulating hover events (jsdom does not simulate SVG pointer events reliably).*
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| Tooltip visually appears on chart hover | IXTN-04 | jsdom cannot simulate SVG pointer events | Hover over donut slices in ExpenseBreakdown and AvailableBalance; verify currency-formatted tooltip appears |
+| Center text in AvailableBalance updates locale | FIX-01 | Visual verification of formatted output | Switch user locale to 'en', verify center text shows `$1,234.56` format; switch to 'de', verify `1.234,56 €` |
+
+---
+
+## 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 < 5s
+- [ ] `nyquist_compliant: true` set in frontmatter
+
+**Approval:** pending