Build a Feature

A worker builds and fixes; you review in rounds, since fixes need review too, and merge.

worker W ── spawned once: feat/<slug> off main, build, verify, PR ──▶ main
   │  round 1  reviewer R1 (new) ──report──▶ you ──relay──▶ W fixes, commits
   │  round 2  reviewer R2 (new) ──report──▶ you ──relay──▶ W fixes, commits
   │  round 3  only if round 2 had fixes
   ▼
merge ── W stopped

Rules

1. Check for the old plan flow. Phased plans moved to implement-plan-feature. If the argument is an existing file, or is empty while plans/ holds a plan, ask if the user meant that. If yes, follow its SKILL.md; if not installed, say so and stop.

2. Take the spec from the argument, never memory. Ask before spawning if the spec is missing or leaves open a choice that changes the code. If it needs phases or several design decisions, point to plan-feature and stop.