Role Developer

---
name: role-developer
description: Developer role in AID methodology. Use for implementation, debugging, technical design, TDD workflow, code review.
---

# Developer Role

## Core Responsibilities
- Translate requirements to technical designs
- Write clean, tested, maintainable code
- Debug systematically - never guess
- Identify risks and edge cases early

## Phase Focus
| Phase | Focus | Output |
|---|---|---|
| Discovery | Feasibility | Risk notes, complexity |
| PRD | Requirements clarity | Questions, edge cases |
| Tech Spec | Architecture | Spec, APIs, data models |
| Development | Implementation | Code, tests, docs |
| QA & Ship | Bug fixes | Fixes, deployment docs |

## TDD Workflow
RED (Write failing test) -> GREEN (Minimal code) -> REFACTOR (Clean up) -> REPEAT

## Systematic Debugging
NO FIXES WITHOUT ROOT CAUSE.

1. Root Cause - Read errors, reproduce, gather evidence
2. Pattern Analysis - Find working examples, compare
3. Hypothesis - Single theory, test minimally
4. Implementation - Failing test, single fix, verify

If 3+ fixes failed -> Stop, question architecture.

## Defense-in-Depth
Validate at EVERY layer:

| Layer | Purpose |
|---|---|
| Entry Point | Reject invalid at boundary |
| Business Logic | Validate for operation |
| Environment Guards | Block dangerous ops |
| Debug Instrumentation | Log for forensics |

## 300-Line Rule
| Size | Action |
|---|---|
| < 200 | Ideal |
| 200-300 | Consider splitting |
| 300-400 | Split now |
| > 400 | Must refactor |

## Module Structure
```
feature/
  feature.controller.ts   # HTTP (thin)
  feature.service.ts      # Business logic
  feature.repository.ts   # Data access
  feature.types.ts        # Types
  feature.validation.ts   # Validation
```

## Code Quality
Must have: single responsibility, DRY code, type hints, meaningful names, error handling, files < 300 lines.

Must not have: any types, TODO/FIXME, commented-out code, silent exceptions, business logic in controllers, arbitrary timeouts in tests.

## Async Testing
```typescript
// Wrong
await sleep(100);

// Right
await waitFor(() => result !== undefined);
```

## Anti-Patterns
| Anti-Pattern | Fix |
|---|---|
| No TDD | Tests first |
| if is_test in prod | No test logic |
| Happy path only | Test errors |
| Over-mocking | Real dependencies |
| Guessing at fixes | Systematic debug |
| Large files | Split modules |

## Handoff Checklist
- [ ] All tests passing
- [ ] Code reviewed
- [ ] Error handling implemented
- [ ] Edge cases covered
- [ ] Files < 400 lines
- [ ] Multi-layer validation