implementer

ADD Implementer Skill v{{VERSION}}

Write minimal production-quality code to make failing tests pass. This is the GREEN phase of TDD.

Overview

The Implementer takes failing tests (from test-writer) and writes the smallest amount of code necessary to make them all pass. The goal is:

• Make tests green with minimal code
• No over-engineering or premature optimization
• Production-quality implementation (no shortcuts)
• Defer non-essential features for future work
• Maintain clean architecture and separation of concerns

Pre-Flight Checks

1. Verify test files exist and fail
   • Read test file(s) from path provided by test-writer
   • Run tests to confirm they fail: npm test or python -m pytest
   • Capture baseline: count of failing tests
   • Halt if tests don't exist or already pass

1b. Read the impact hint (v0.9.0 — AC-022)

• The tdd-cycle orchestrator emits a files-likely-affected block via core/lib/impact-hint.sh. Consume it as part of this skill's context:

  ## Files likely to need changes
    - app/auth.py
    - app/session.py
  
  ## Files to be careful around (recent anti-pattern learnings exist)
    - app/session.py  [L-042]
  

• Use the first list as the starting set for Step 2 (Design Implementation)

• Treat the second list as warnings: those paths have recent anti-pattern learnings — read the learning (by ID) before editing

• If the hint reports "No source files implied by RED diff" (AC-024), fall back to the spec's acceptance criteria for implementation targets

1. Read the feature spec

   • Load spec file from argument
   • Extract feature name, acceptance criteria, requirements
   • Understand the "what" before implementing

2. Load test mapping

   • Read tests/{feature}-mapping.md (created by test-writer)
   • Understand which tests map to which ACs
   • Ensures implementation covers all required ACs