Use when adding or editing a GitHub Actions workflow, composite action, or reusable workflow under `.github/` — new CI jobs, triggers, matrices, checkout/clone tuning, action pinning, GitHub App token auth, concurrency groups, `timeout-minutes`, `paths` filters, caching, or runner choice. Covers PostHog's workflow-authoring conventions and the reasons behind them: the 500-runs/10s dispatch cap, shallow vs full clone, per-SHA push concurrency, dedicated App-token rate-limit buckets, and fork-safe secrets on a public repo. Points to the linters (`bin/hogli lint:workflows`, actionlint) that enforce the mechanical rules, and to the narrower skills for production deploys, secrets, and Depot runners. Not for debugging red CI (use debugging-ci-failures) or wiring a new secret end to end (use managing-github-actions-secrets).