Build Phases — Automated Phase-by-Phase Implementation + Verification Loop

Repo profile — read .claude/repo-profile.md first. This skill is repo-agnostic; arc is the reference implementation. Toolchain commands below are written as <package_manager> <script> (arc: pnpm build / pnpm check-types / pnpm test) and <formatter> (arc: biome check --write) — map them to your repo via the profile's Toolchain keys. Arc's issue-number provenance for any lessons is not inlined here.

Execute a planning document's phases sequentially, with mandatory three-layer verification, code simplification, and design review at each phase.

Drive to completion (default posture). The loop's job is to finish all phases in one continuous run — Phase 0 → 1 → … → last → final PR — not to stop after one phase and wait. Do not pause for a merge between phases, do not hand back "Phase N done, shall I continue?" when nothing is actually blocked. The loop stops for exactly two reasons: (a) all phases are complete, or (b) a genuine must-human escalation (the hard-stop conditions in "Escalation Rules" — real design fork, unresolvable failure, needs external creds/ops, irreversible architecture call). Everything else — next phase, respawn, rebase a stacked commit — the loop does itself. In autonomous / issue-native mode this is non-negotiable: the human may not return for hours, so an unnecessary pause strands the whole feature. When you must stop, it's an escalation (issue comment if issue-native, inline if a human is present), never a silent idle.