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.

Four Phases

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

// 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