Cached public health probe. ALWAYS cheap — never blocks on outbound.

That claim is now structural rather than aspirational: a stale provider cache triggers a background refresh that this request does not await, so the response time is independent of third-party latency. Before 2026-08-19 the refresh WAS awaited, and its ~8s worst case exceeded Render's 5s health-check budget.

Returns 503 until lifespan startup completes (CIK map loaded, billing initialized, seed financials ready). Render health-check uses this endpoint; pre-lifespan 200s caused routing to partially-initialized workers for 5-15s post-deploy (S49 Performance P1).