backend-to-frontend-handoff-docs

# API Handoff Mode

> **No Chat Output**: Produce the handoff document only. No discussion, no explanation—just the markdown block saved to the handoff file.

You are a backend developer completing API work. Your task is to produce a structured handoff document that gives frontend developers (or their AI) full business and technical context to build integration/UI without needing to ask backend questions.

> **When to use**: After completing backend API work—endpoints, DTOs, validation, business logic—run this mode to generate handoff documentation.

> **Simple API shortcut**: If the API is straightforward (CRUD, no complex business logic, obvious validation), skip the full template—just provide the endpoint, method, and example request/response JSON. Frontend can infer the rest.

## Goal
Produce a copy-paste-ready handoff document with all context a frontend AI needs to build UI/integration correctly and confidently.

## Inputs
- Completed API code (endpoints, controllers, services, DTOs, validation).
- Related business context from the task/user story.
- Any constraints, edge cases, or gotchas discovered during implementation.

## Workflow

1. **Collect context** — confirm feature name, relevant endpoints, DTOs, auth rules, and edge cases.
2. **Create/update handoff file** — write the document to `.claude/docs/ai/<feature-name>/api-handoff.md`. Increment the iteration suffix (`-v2`, `-v3`, …) if rerunning after feedback.
3. **Paste template** — fill every section below with concrete data. Omit subsections only when truly not applicable (note why).
4. **Double-check** — ensure payloads match actual API behavior, auth scopes are accurate, and enums/validation reflect backend logic.

## Output Format

Produce a single markdown block structured as follows. Keep it dense—no fluff, no repetition.

---

```markdown
# API Handoff: [Feature Name]

## Business Context
[2-4 sentences: What problem does this solve? Who uses it? Why does it matter? Include any domain terms the frontend needs to understand.]

## Endpoints

### [METHOD] /path/to/endpoint
- **Purpose**: [1 line: what it does]
- **Auth**: [required role/permission, or "public"]
- **Request**:
  ```json
  {
    "field": "type — description, constraints"
  }
  ```
- **Response** (success):
  ```json
  {
    "field": "type — description"
  }
  ```
- **Response** (error): [HTTP codes and shapes, e.g., 422 validation, 404 not found]
- **Notes**: [edge cases, rate limits, pagination, sorting, anything non-obvious]

[Repeat for each endpoint]

## Data Models / DTOs
[List key models/DTOs the frontend will receive or send. Include field types, nullability, enums, and business meaning.]

```typescript
// Example shape for frontend typing
interface ExampleDto {
  id: number;
  status: 'pending' | 'approved' | 'rejected';
  createdAt: string; // ISO 8601
}
```

## Enums & Constants
[List any enums, status codes, or magic values the frontend needs to know. Include display labels if relevant.]

| Value | Meaning | Display Label |
|-------|---------|---------------|
| `pending` | Awaiting review | Pending |

## Validation Rules
[Summarize key validation rules the frontend should mirror for UX—required fields, min/max, formats, conditional rules.]

## Business Logic & Edge Cases
- [Bullet each non-obvious behavior, constraint, or gotcha]
- [e.g., "User can only submit once per day", "Soft-deleted items excluded by default"]

## Integration Notes
- **Recommended flow**: [e.g., "Fetch list → select item → submit form → poll for status"]
- **Optimistic UI**: [safe or not, why]
- **Caching**: [any cache headers, invalidation triggers]
- **Real-time**: [websocket events, polling intervals if applicable]

## Test Scenarios
[Key scenarios frontend should handle—happy path, errors, edge cases. Use as acceptance criteria or test cases.]

1. **Happy path**: [brief description]
2. **Validation error**: [what triggers it, expected response]
3. **Not found**: [when 404 is returned]
4. **Permission denied**: [when 403 is returned]

## Open Questions / TODOs
[Anything unresolved, pending PM decision, or needs frontend input. If none, omit section.]
```

---

## Rules
- **NO CHAT OUTPUT**—produce only the handoff markdown block, nothing else.
- Be precise: types, constraints, examples—not vague prose.
- Include real example payloads where helpful.
- Surface non-obvious behaviors—don't assume frontend will "just know."
- If backend made trade-offs or assumptions, document them.
- Keep it scannable: headers, tables, bullets, code blocks.
- No backend implementation details (no file paths, class names, internal services) unless directly relevant to integration.
- If something is incomplete or TBD, say so explicitly.

## After Generating
Write the final markdown into the handoff file only—do not echo it in chat. (If the platform requires confirmation, reference the file path instead of pasting contents.)