GitHub App Checks API replaces injected CI workflows for platform feedback on managed repos (zero Actions billing)

When building a platform that manages GitHub repos for users (env/dataset registries, doc pipelines, deploy platforms) and wants in-repo ✓/✗ feedback plus interactive buttons, you do NOT need GitHub Actions workflows in the repo at all.

Key facts (verified against GitHub docs, 2026):

1. A GitHub App with checks: write can create/update check runs directly via POST /repos/{owner}/{repo}/check-runs — they render identically to CI checks on commits/PRs, with markdown summaries and file/line annotations. Only GitHub Apps can create check runs (OAuth apps and users cannot).
2. Check runs support up to 3 actions buttons (requested actions). Clicking one fires a check_run.requested_action webhook to the App with requested_action.identifier — this is a native in-repo "Run verification" / "Deploy" / "Publish" button with no workflow file.
3. GitHub's "Re-run" UI button fires check_run.rerequested — free re-run semantics.
4. Billing angle: Actions minutes are billed to the account that OWNS the repo, and are free only for public repos. If your platform owns private repos for users, injected workflows put the CI bill on you, with only org-wide (not per-repo/team) spending controls. Doing validation server-side (webhook push → fetch tree via installation token → lint in your own worker) and posting results via the Checks API eliminates the bill entirely while keeping the native GitHub UX.
5. Heavy execution can be dispatched to external sandboxes (Daytona/Modal/Beam etc.) from your own job queue, with check-run status transitions (queued → in_progress → completed) mirroring job state.

Caveat: check runs created by the GitHub Actions app itself won't trigger check_run-event workflows, but checks created by a different (your) App can. Keep OIDC-based attestation (verify workflow JWTs from token.actions.githubusercontent.com against repo/sha claims) as an optional lane for users who run their own CI and want to report results back.