Run the service-level objectives baseline

Code the narrow path that serves reliability owner gating releases on error budget: accept → authorize/normalize → call dependency → validate → record. Keep stages named so a trace can show which boundary passed. Success must emit evidence useful to slo:availability:ratio and burn_rate1h, not only a 200 with prose. Predict the observable for POST /v1/support/answer before running: 3% provider timeout for 20m trips fast-burn; monthly budget math matches calc-budget.py.

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 AI support-answer service with 99.5% availability + TTFT SLO — resist adding unrelated features mid-path.

For SLO lab, paste the CLI/HTTP transcript beside your prediction for POST /v1/support/answer. If the oracle is unmet (3% provider timeout for 20m trips fast-burn; monthly budget math matches calc-budget.py), 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 SLO-VANITY-200-18.

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 slo:availability:ratio and burn_rate1h. 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 reliability owner gating releases on error budget 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 AI support-answer service with 99.5% availability + TTFT SLO, the human stakeholder is reliability owner gating releases on error budget, and the incident id you design against is SLO-VANITY-200-18. Re-state the oracle in your notes — 3% provider timeout for 20m trips fast-burn; monthly budget math matches calc-budget.py — and keep the invariant visible: bad events include malformed upstream + timeout fallbacks; auth 4xx excluded. Track slo:availability:ratio and burn_rate1h as the scoreboard. Surface under change control: POST /v1/support/answer. If you only have forty minutes, finish the fixture for HTTP 200 fallbacks counted as good while citations empty — vanity availability before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.