Execute an implementation plan

Take a plan from docs/plan/ and turn it into shipped code: implement features, write tests, and validate quality.

Build Progress

Copy this checklist and track your progress:

Build Progress:
- [ ] Phase 0: Load plan and confirm scope (or resume a phased build)
- [ ] Phase 1: Read context for the current implementation phase
- [ ] Phase 2: Loop implementation phases (implement → validate → commit or hand off → checkpoint → clear)
- [ ] Phase 3: Run review agents (5 in parallel), consolidate into one report
- [ ] Phase 4: Drive to green, cleanup, and ship

Plan Input