developer

Implementation agent that writes production code following approved plans with strict TDD and self-healing.

Overview

The developer writes production code in Phase 3 (Build GREEN). It reads the approved plan, confirms failing tests exist, then implements until all tests pass. The developer follows existing codebase patterns (no new patterns without an ADR), enforces type safety (no any types), and self-heals up to 3 times when tests fail — each attempt using a different approach. After 3 failures, it escalates.

The developer exclusively owns src/, lib/, app/ — no other agent touches production code.

Quick Reference

Development & Implementation

Rule	Enforcement
TDD strict	Will not write code without failing tests from tester
Plan required	Reads tasks/plans/YYMMDD-name.md before starting
No any types	Type-safe code enforced (no any, no unsafe casts)
Pattern respect	Follows existing codebase patterns; new patterns need ADR
Self-healing	Up to 3 fix attempts with different approaches per failure
Escalation	After 3 failures: reports what was tried + suspected root cause

File Ownership

Exclusively owns: src/, lib/, app/ directories (all production code).

How to Use

The developer is invoked automatically after the tester confirms failing tests exist. You don't call it directly.

Developer receives:
  Plan: tasks/plans/260327-auth.md
  Failing tests: tests/auth.test.ts (12 tests, all red)

Developer works:
  "Reading plan... implementing auth middleware..."
  "Tests failing: 3 remaining... self-healing attempt 1..."
  "All 12 tests pass. Implementation complete."

Developer hands off:
  → Tester (green phase verify) → Reviewer

Under the Hood

Self-Healing Pattern

When tests fail after implementation:

Attempt 1: Fix based on test error message
Attempt 2: Different approach (alternative algorithm/pattern)
Attempt 3: Minimal implementation (simplest possible solution)
Escalation: Report failing output + what was tried + suspected root cause

Each attempt must use a different approach — not retry the same fix.

Handoff Example

Developer → Tester (green verify):
  Files modified: src/middleware/auth.ts, src/services/token.ts
  Files created: src/utils/jwt-helper.ts
  Test results: 12/12 passing
  Plan deviations: None
  New patterns: None (used existing middleware pattern)

Troubleshooting

Issue	Cause	Fix
"No failing tests found"	Tester hasn't run red phase	Wait for tester to complete Phase 2
"No approved plan"	Gate 1 not passed	Approve the plan first
Self-healing exhausted (3 attempts)	Likely a plan/test mismatch	Escalated — check if plan needs revision or tests need updating
New pattern introduced without ADR	Developer shouldn't do this	Route to architect to evaluate and create ADR