Run the disaster recovery baseline

Code the narrow path that serves DR lead failing over region A → B within RTO 2h / RPO 15m: accept → authorize/normalize → call dependency → validate → record. Keep stages named so a trace can show which boundary passed. Success must emit evidence useful to rto_minutes, rpo_minutes, citation_precision_post_restore, not only a 200 with prose. Predict the observable for region-b https://b.rag.example before running: drill DR-2026-07-30: restore completes 97m; gold citation_precision ≥ 0.95.

Drive the path with recording fakes or local stubs. Assert call order and arguments. Idempotency keys or stable ids should keep retries from duplicating costly work where the product requires it. Product under test remains regional RAG platform restore with PostgreSQL + object storage + vector indexes — resist adding unrelated features mid-path.

For Disaster recovery lab, paste the CLI/HTTP transcript beside your prediction for region-b https://b.rag.example. If the oracle is unmet (drill DR-2026-07-30: restore completes 97m; gold citation_precision ≥ 0.95), stop and debug this page; do not compensate with prompt folktales. Re-run once after a clean process start to catch hidden global state that would invalidate DR-2026-07-30.

Performance sketch: measure local p95 for the fake-backed path so later regressions are obvious. Keep concurrency modest until failure-handling proves limits. Log a single structured event per success with request id, revision, and the evidence field behind rto_minutes, rpo_minutes, citation_precision_post_restore. Avoid hidden global caches in the happy path unless the lab is about caching — and even then key by tenant. If the path calls a model, pin model id in config and echo it in the response for auditability. Remember DR lead failing over region A → B within RTO 2h / RPO 15m experiences wall-clock time, not your debugger’s single-step comfort.

Prefer explicit function names over a single god-object handleRequest. Thread a correlation id from ingress to the last log line. When streaming, define what partial failure means before coding. Snapshot one successful response body in fixtures after redaction. If the path writes to a queue, assert message attributes in the fake. Stop adding retries on this page; that is the next concern. 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.