hive-jobq-metrics

OTEL export of a hive-jobq graph's state rollup, using the same hive-jobq-wire state_rollup() counts a viewer's /rollup endpoint would serve — ridden out to the collector on a timer instead of only on request.

Why this is not part of hive-jobq or hive-jobq-wire. Both of those crates are dependency-light on purpose (no tokio, no HTTP client) — the scheduler is logic, the wire crate is presentation, and neither wants to drag the OTEL SDK, an async runtime, and an OTLP HTTP client into every consumer that just wants to run a graph or serialize one to JSON. Metrics export is a third concern with its own weight, so it gets its own crate rather than bloating either of theirs.

spawn_exporter is generic over hive_jobq::scheduler::Scheduler<N, R> — any host's jobq instance can call it, not just one hardcoded caller. It holds no process-global state: call it once per graph you want exported, and keep the returned SdkMeterProvider alive for as long as export should continue (dropping it stops the PeriodicReader).