- `service` node type: command, port, worker label, health path, env and
weights (an artifact digest the worker fetches as {weights}). Its flow
starts it; it restarts with backoff, reads degraded while starting or
without a worker and down after three starts that never got healthy, and
publishes http://<worker>:<port> once /health answers 200, "" when it ends.
- Worker protocol 3: a `serve` call, every call in its own process group,
killed when the engine ends the call, the socket drops or the agent gets
SIGTERM. `--service-host` overrides the address the engine sees.
- Services and compiles take no `--parallel` slot, and a flow's detail is
built off the event loop, so a save no longer stalls the engine.
Melvin Strobl
85dad39973