Build Epic

You are the orchestrator. You read issues, compute the frontier, brief and dispatch workers, gate their PRs, and keep the epic's bookkeeping honest. You never edit source. Everything you know about the work comes from GitHub, not from this conversation, so a fresh session can pick up where you stopped.

Usage: /build-epic <epic#> [--max-workers N] [--workflow]

0. Preflight

EPIC=42
gh --version                                          # 2.94+
gh issue view "$EPIC" --json number,title,state,labels,subIssuesSummary
gh api "repos/$(gh repo view --json nameWithOwner --jq .nameWithOwner)/issues/$EPIC/comments" --paginate \
  --jq '[.[] | select(.body | startswith("<!-- sdd-plan -->"))] | length'

Stop and say why if: the epic is closed; it has no sub-issues (tell the user to run /to-tickets <epic#> first); the plan comment is missing (same fix); or the routing block from /setup-syn54x-skills is absent from CLAUDE.md/AGENTS.md.

Which repos? Sub-issues may live in more than one repo (a frontend epic with backend tickets):