implement

name	implement
description	Implements use cases and fixes bugs by creating Next.js pages, components, API route handlers, and server actions. Use when the user asks to "implement a use case", "fix a bug", "build the UI", "create an API endpoint", "write a page", or mentions Next.js implementation, App Router, server actions, or full-stack implementation.

Implement Use Case

Instructions

Implement $ARGUMENTS using Next.js App Router for both the UI and API layer. $ARGUMENTS can be a use case (UC-XXX), a technical task (TT-XXX), or a bug fix (BUG-XXX). Write unit tests alongside the implementation. Integration tests (vitest-test) and e2e tests (playwright-test) are separate skills.

Use the context7 MCP server to look up Next.js documentation when needed.

DO NOT

• Create integration or e2e tests (use dedicated testing skills instead)
• Use the Pages Router (use App Router exclusively)
• Use raw SQL queries (use Prisma Client)
• Use client components when server components suffice
• Put database calls in client components or API routes called only by server components
• Make implementation decisions without documenting their provenance (EXPLICIT vs INFERRED)
• Over-engineer — implement only what the specification requires. No speculative abstractions, unnecessary indirection, premature generalisation, or features not in the spec. Three similar lines of code are better than a premature abstraction. If a simple approach satisfies the requirement, use it.

Nexa Rules Gate

Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/NEXA_RULES_GATE.md.

Sprint Branch Gate

Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/SPRINT_BRANCH_GATE.md.

Project Readiness Gate

Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/PROJECT_READINESS.md.

This gate checks that cross-cutting infrastructure (middleware, error logging, security headers, environment configuration) exists before use case implementation begins. It applies to UC-XXX items only — TT-XXX and BUG-XXX items skip this gate.

Do not proceed with implementation until all items pass or the user explicitly waives failures.

DoR Check

• For UC-XXX: Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/DEFINITION_OF_READY.md.
• For TT-XXX: Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/DEFINITION_OF_READY_TT.md.
• For BUG-XXX: Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/DEFINITION_OF_READY_BUG.md.

Do not proceed with implementation until all items pass or the user explicitly waives failures.

Tracking

Read and follow the Before Implementation steps in ${CLAUDE_PLUGIN_ROOT}/shared/tracking/TRACKING.md.

Test Data Conventions

• Use only example.com for test emails and accounts (e.g., [e-mail], [e-mail]). This is an IANA-reserved domain that will never route real mail.

Workflow

1. Read the specification:
   • For UC-XXX: Read the use case specification from docs/use_cases/
   • For TT-XXX: Read the technical task specification from docs/technical_tasks/
   • For BUG-XXX: Read the bug report from docs/bugs/
2. Read the entity model from docs/entity_model.md (if applicable)
3. Read the design artifact from docs/designs/ (if it exists for this UC). When a design artifact exists, the implementation must match the specified screens, layout, components, states, and navigation flow.
4. Read project design rules from docs/designs/DESIGN_RULES.md (if it exists). These are project-specific constraints — e.g., shared layout elements (header, footer, sidebar), mandatory components, or navigation patterns — that every implementation must follow. Missing a shared element specified in design rules is a defect.
5. Check existing code for patterns and conventions
6. i18n Detection — Always check whether the project uses internationalization. First, check the project's CLAUDE.md for the marker <!-- NEXA_I18N_CONFIGURED -->. If absent, fall back to looking for i18n indicators: translation/message files, i18n configuration, locale directories, translation function imports (useTranslations, getTranslations, t(), intl, etc.), locale-based routing segments ([locale], [lang]), or i18n libraries in package.json (e.g., next-intl, react-intl, react-i18next, i18next). If any i18n setup is found, all user-facing strings in this implementation MUST use the project's established translation pattern:
   • Study how existing pages use translations and follow the same pattern
   • For every new page or section, add translation keys to all locale files following the project's existing file structure and naming conventions
   • User-facing error messages in server actions and API route handlers must also use translation keys, not hardcoded strings
   • Use the project's localized navigation utilities if they exist, instead of raw framework imports
   • Place new pages under the locale route segment if the project uses locale-based routing
7. Implement API route handlers (if needed for client-side fetching):
   • Create route handlers in app/api/**/route.ts
   • Export named functions matching HTTP methods (GET, POST, PUT, DELETE)
   • Validate request bodies with zod
   • Use Prisma Client for data access
   • Return NextResponse.json() with appropriate status codes
8. Implement server actions (if needed for form mutations):
   • Create actions in app/actions/ or colocate with the page
   • Mark with "use server" directive
   • Validate input with zod
   • Use Prisma Client for data access
   • Call revalidatePath() or revalidateTag() for cache invalidation
9. Implement the UI:
   • Create or update page.tsx and layout.tsx files
   • Use server components by default for data fetching with Prisma
   • Use client components ("use client") only for interactivity (forms, event handlers, state)
   • Create reusable UI components in components/
   • Handle loading states with loading.tsx
   • Handle errors with error.tsx
   • Handle empty states
   • When a design artifact exists, match the specified layout, components, states, and navigation
   • When project design rules exist (read in step 4), enforce every rule — e.g., include shared layout elements, follow mandatory navigation patterns, and apply required brand guidelines
   • When i18n is active (detected in step 6), every user-facing string must use the project's translation pattern — no hardcoded text in JSX
   • When implementing forms where users enter data, always add client-side and server-side validation:
     • Define a zod schema for each form's input fields
     • Apply client-side validation to show inline field errors before submission
     • Validate again on the server side in the server action or API route handler (never trust client-only validation)
     • Display server-side validation errors back to the user
10. Write unit tests for the implemented logic:
    • Test API route handlers with mocked Prisma Client
    • Test server actions with mocked dependencies
    • Test client components with React Testing Library
    • When forms are involved, write dedicated validation unit tests:
      • Test the zod schema directly: valid inputs pass, invalid inputs produce the expected errors
      • Test that server actions and API route handlers reject invalid input and return appropriate error responses
      • Test that form components display validation errors for invalid input
    • Run tests with npx vitest run to verify they pass
11. Run the /code-quality skill
12. Verify the implementation compiles successfully with next build
13. Document implementation decisions in a DECISIONS.md file (or in the PR description):
    • For each non-trivial decision made during implementation, record:
      • Decision: What was decided
      • Provenance: EXPLICIT (from spec/requirements) or INFERRED (agent reasoning)
      • Source/Reasoning: Quote the source document or explain the reasoning
    • INFERRED decisions are candidates for stakeholder review before merge

Post-Implementation Tracking

Read and follow the After Implementation steps in ${CLAUDE_PLUGIN_ROOT}/shared/tracking/TRACKING.md.

Resources

• Use the context7 MCP server for Next.js documentation