Liveness, plus how stale the mirror is.
Overview
The ONLY endpoint that answers before a world exists. It reports
world_ready: false rather than 503, because the process really is up and
a monitoring system should be able to tell "booting" from "dead".
Code example
curl -X GET "https://example.com/health"Response example
{ "status": "string", "world_ready": true, "age_ms": 0, "publish_seq": 0}Response body
200Runner is up. `world_ready` is false until the first mirror publish.application/json
GET /health body. The only endpoint that answers before a world exists,
which is why sim_time_ns is optional here and mandatory everywhere else.