Configure the disaster recovery contract

Implement types or schemas around region-b https://b.rag.example so illegal states are unrepresentable at the boundary. For regional RAG platform restore with PostgreSQL + object storage + vector indexes, trusted inputs come from sessions, signatures, pinned digests, or workload identity — not from free-form model text. DR lead failing over region A → B within RTO 2h / RPO 15m should be able to read the contract and know which fields are optional, which are enumerated, and which abort the request. Constructors and boot paths must not perform provider side effects; injection points keep tests honest.

Document required env vars in .env.example with placeholders only. Rotation story belongs later, but the contract already forbids printing secrets and forbids defaulting to fail-open when a dependency is missing. Invariant to encode in types/tests: restore validates citation gold set before traffic; corrupt snapshot rejected. If a config number lacks units, fix the name (timeout_ms, rpm_hard) before writing logic.

Create fixtures for the golden path and for DR-2026-07-30. Name files after the behavior (429-retry-after.json, cross-tenant.json, empty-citation.json) rather than test1. Each fixture carries expected status/code. This kit is the shared language for validation and failure pages.

Compatibility promise: additive fields may appear only if readers ignore unknowns safely; breaking changes bump a version visible on the wire. For AI payloads, size limits arrive before JSON parse when hostile blobs are a risk. Document how clock skew, idempotency keys, and tracing headers travel through regional RAG platform restore with PostgreSQL + object storage + vector indexes. If you use feature flags later, the contract already states that flags are not authorization. Link each config knob to a unit and a failure mode (“0 means disabled” vs “0 means divide-by-zero”). A peer reviewing the PR should find DR-2026-07-30 named in a comment on the adversarial fixture.

Generate OpenAPI or a typed client only after the hand schema is stable for one fixture round-trip. Record how errors look on the wire — problem+json, envelope, or bare status — and stick to one. Clock sources must be injectable for skew tests. If webhooks appear later, document signature header names now even as TODOs. Keep sample payloads UTF-8 and free of real emails. Add a makefile or npm script that validates schemas without network. In this chapter the product is regional RAG platform restore with PostgreSQL + object storage + vector indexes, the human stakeholder is DR lead failing over region A → B within RTO 2h / RPO 15m, and the incident id you design against is DR-2026-07-30. Re-state the oracle in your notes — drill DR-2026-07-30: restore completes 97m; gold citation_precision ≥ 0.95 — and keep the invariant visible: restore validates citation gold set before traffic; corrupt snapshot rejected. Track rto_minutes, rpo_minutes, citation_precision_post_restore as the scoreboard. Surface under change control: region-b https://b.rag.example. If you only have forty minutes, finish the fixture for traffic cut before vector rebuild finishes — fluent ungrounded answers before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.