Prove behavior with deterministic tests

Add executable validation at the trust boundaries of answer API + indexer sharing provider key via versioned secrets manager. Reject unknown fields where they matter, bound string sizes, and coerce only after auth/signature checks when raw bytes are security-relevant. Invariant under test: dual-key window: readers accept v1+v2; revoke v1 only after emit proves zero v1 use for 30m. A TypeScript type or Python annotation is not runtime validation — pair them with parsers.

Automate the fixtures from setup, including a recreation of SEC-REVOKE-EARLY-21. Assert both the visible error and the absence of side effects (no provider call, no queue write, no flag flip). Where metrics matter, assert label enums stay bounded.

Document which failures are client mistakes (4xx) versus operator/config mistakes (5xx/503). Oracle still stands: rotate to v2 → deploy → traffic on v2 → revoke v1 with audit event ROT-2026-07-30. Validation should make accidental “success with empty body” impossible for security engineer rotating openai/prod after contractor offboarding.

Property ideas: shuffled field order, Unicode edges, maximum-length strings, and replayed timestamps. Where money, identity, or citations matter, assertion messages should cite the field name. Do not snapshot entire provider payloads in tests; assert semantically. If validation fails open “to keep the demo working,” you have inverted the lab. Tie at least one CI job to the SEC-REVOKE-EARLY-21 fixture so main cannot regress silently. Re-read dual-key window: readers accept v1+v2; revoke v1 only after emit proves zero v1 use for 30m after each new parser — convenience helpers love to bypass it.

Table-drive status codes and error codes so reviewers see coverage at a glance. Include a Unicode normalization case if user text is accepted. Verify that oversized bodies fail before CPU-heavy work. Where digests or versions are pinned, assert mismatch behavior. Keep golden files small enough to read in review. CI should fail on skipped tests that mark the incident fixture as xfail without a ticket link. In this chapter the product is answer API + indexer sharing provider key via versioned secrets manager, the human stakeholder is security engineer rotating openai/prod after contractor offboarding, and the incident id you design against is SEC-REVOKE-EARLY-21. Re-state the oracle in your notes — rotate to v2 → deploy → traffic on v2 → revoke v1 with audit event ROT-2026-07-30 — and keep the invariant visible: dual-key window: readers accept v1+v2; revoke v1 only after emit proves zero v1 use for 30m. Track secret_version_share and auth_fail_rate as the scoreboard. Surface under change control: secrets manager path openai/prod. If you only have forty minutes, finish the fixture for revoke v1 while indexer still cached v1 → 401 storm before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.