Constrain access and rehearse rollback

Separate runtime and operator roles for FastAPI receiver for batch-index completion events → durable queue. Runtime may only perform the narrow actions that indexer worker waiting on provider batch.completed callbacks needs; operators get audited break-glass with TTL. Encode a negative probe that denies the privilege trick related to signature optional in staging config accidentally shipped to prod.

Redact prompts/PII at collection. Secrets enter via a manager or workload identity — never source, fixtures, or exception strings. Incident HOOK-SIG-OFF-16 should be impossible if these controls hold. Output allowlists and schema checks stay in force on error paths.

Rehearse the rollback or kill switch timed against a clock. Record actor, reason, prior revision/secret/flag, and verification query. Invariant reminder: verify HMAC signature + timestamp skew ≤ 5m; enqueue idempotent by event_id.

Abuse cases unique to this lab include the privilege path implied by signature optional in staging config accidentally shipped to prod. Prove a read-only role cannot mutate. Break-glass tokens expire; leftover tokens fail the drill. Dependency pin/digest story matters when images or models move under you. Document how to rotate the credential that FastAPI receiver for batch-index completion events → durable queue uses without a full outage window longer than your dual-run plan. Security evidence is part of ship, not an appendix nobody reads.

List network egress destinations and justify each. Ensure debug endpoints are off by default in the shipping config. Verify that error responses do not echo secrets or raw stack frames to clients. For multi-tenant paths, add a cross-tenant probe fixture. Time the rollback drill twice — once with the author, once with a peer. Store the drill transcript beside the threat notes for the incident id. In this chapter the product is FastAPI receiver for batch-index completion events → durable queue, the human stakeholder is indexer worker waiting on provider batch.completed callbacks, and the incident id you design against is HOOK-SIG-OFF-16. Re-state the oracle in your notes — valid event → 202 + one queue message; replay same event_id → 202 no duplicate work — and keep the invariant visible: verify HMAC signature + timestamp skew ≤ 5m; enqueue idempotent by event_id. Track webhook_accept_total and duplicate_suppressed_total as the scoreboard. Surface under change control: POST /webhooks/batch-index. If you only have forty minutes, finish the fixture for signature optional in staging config accidentally shipped to prod before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.