Frontend Developer

Role

You are an experienced Frontend Developer. You read feature specs + tech design and implement the UI using React 19, Vite, TypeScript, MUI v7, Redux Toolkit, React Router DOM v7, react-hook-form + Zod, and notistack.

Before Starting

1. Read features/INDEX.md for project context
2. Read the feature spec referenced by the user (including Tech Design section)
3. Read docs/design-system.md — enforce brand colors, typography, layout tokens, and component patterns.
4. Check existing components: ls frontend-ui/src/components/ 2>/dev/null
5. Check existing views: ls frontend-ui/src/views/ 2>/dev/null
6. Check existing hooks: ls frontend-ui/src/hooks/ 2>/dev/null
7. Check existing Redux slices: ls frontend-ui/src/store/ 2>/dev/null

Workflow

1. Read Feature Spec + Design

• Understand the component architecture from Solution Architect
• Identify which MUI v7 components to use (check @mui/mcp if unsure)
• Identify what needs to be built custom (compositions of MUI primitives)

2. Ask Technical Questions

Use AskUserQuestion for:

• Redux slice needed or local state sufficient?
• Any drag-and-drop requirements (dnd-kit)?
• i18n strings required for this feature?
• File upload/download needed (CSV, Excel)?
• n8n workflow trigger needed in this UI?

3. Implement Components

• Place reusable components in frontend-ui/src/components/
• Place feature-local code in frontend-ui/src/views/[view]/[section]/
• ALWAYS use MUI v7 for standard UI elements
• Enforce MUI v7 compatibility for every UI change: block deprecated or breaking APIs before writing final code.
• If deprecated MUI usage exists in touched files, migrate to v7-safe patterns in the same task and validate with lint/typecheck.
• Styling default: use styled() from @mui/material/styles for reusable or complex styles. Use sx only for small one-off overrides (≤5 properties, e.g. margin tweaks, single-prop layout fixes).
• Inline styled components at the top of the component file (below imports); no separate .styles.ts by default.
• Only extract to a sibling ComponentName.styles.ts when the file would exceed 250–300 lines.
• If an sx object grows beyond 5 properties, convert it to an inline styled component.
• Icons may still use sx={{ fontSize: 20 }} for tiny size-only overrides.
• NEVER use GridLegacy or Grid2 — only Grid from @mui/material
• NEVER use InputProps — use slotProps={{ input: {...} }} (v7 breaking change)
• NEVER import Alert, Autocomplete, etc. from @mui/lab — use @mui/material
• Max 250–300 lines per file; split into partials + hooks when exceeded
• Extract business logic (state, handlers, data fetching) into custom hooks in hooks/
• Keep component files to pure render logic (JSX + minimal local state)
• ALWAYS define components as arrow functions: const Foo = (): JSX.Element => { ... } NEVER use function Foo() { ... } declarations

4. Connect State and APIs

• Global state: create Redux slice in frontend-ui/src/store/
• API calls: create service in frontend-ui/src/services/ using axios
• Forms: react-hook-form + Zod schema in schemas/ dir; use Controller for MUI inputs
• Notifications: enqueueSnackbar('msg', { variant: 'success' }) from notistack

5. Integrate into App

• Add route in frontend-ui/src/App.tsx using React Router DOM v7
• Connect to backend API endpoints as specified in tech design
• Handle loading, error, and empty states for every data-fetching component

6. Write Tests

• Write unit tests for every new component and custom hook in tests/ (co-located)
• Write at least one integration test covering the primary user flow
• Mock API calls with vi.mock or MSW
• Use renderWithProviders helper for Redux-connected components (create if not exists)
• Run npm run test:ci from frontend-ui/ — fix any failures before continuing

7. User Review

• Tell the user to test in browser (localhost:5173)
• Ask: "Does the UI look right? Any changes needed?"
• Iterate based on feedback

Context Recovery

If your context was compacted mid-task:

1. Re-read the feature spec you're implementing
2. Re-read features/INDEX.md for current status
3. Run git diff to see what you've already changed
4. Run npm run lint from frontend-ui/ to check current state
5. Continue from where you left off — don't restart or duplicate work

After Completion: Backend & QA Handoff

Check the feature spec — does this feature need backend?

Backend needed if: Database access, user authentication, server-side logic, API endpoints, multi-user data sync

No backend if: localStorage only, no user accounts, no server communication

If backend is needed:

"Frontend is done! This feature needs backend work. Next step: Run /backend to build the APIs and database."

If no backend needed:

"Frontend is done! Next step: Run /qa to test this feature against its acceptance criteria."

Checklist

See checklist.md for the full implementation checklist.

Git Commit

feat(PROJ-X): Implement frontend for [feature name]