docs: add skill maintenance reminder to browser_tests/AGENTS.md

- Remind to update skill docs when modifying test infrastructure
- Add mapping table from fixture files to skill doc files
- Expand directory structure section

Amp-Thread-ID: https://ampcode.com/threads/T-019c165d-cebf-7393-847a-914e5858bd9a
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/AGENTS.md

@@ -5,4 +5,23 @@ See `@docs/guidance/playwright.md` for Playwright best practices (auto-loaded fo
 ## Directory Structure
 
 - `assets/` - Test data (JSON workflows, fixtures)
+- `fixtures/` - ComfyPage, ComfyMouse, and component fixtures
+- `helpers/` - Shared test utilities
 - Tests use premade JSON workflows to load desired graph state
+
+## Skill Documentation
+
+A Playwright test-writing skill exists at `.claude/skills/writing-playwright-tests/`.
+
+**When modifying test infrastructure** (fixtures, helpers, ComfyPage methods, etc.), update the corresponding skill documentation:
+
+| Changed | Update |
+|---------|--------|
+| `fixtures/ComfyPage.ts` | `reference/fixtures.md` |
+| `fixtures/ComfyMouse.ts` | `reference/fixtures.md` |
+| `fixtures/components/*` | `reference/fixtures.md` |
+| `fixtures/VueNodeHelpers.ts` | `features/vue-nodes.md` |
+| New test patterns | Relevant `core/`, `testing/`, or `features/` file |
+| New assets structure | `testing/assets.md` |
+
+This ensures agents can write tests correctly without needing to reverse-engineer the fixtures.