ARCP carries observability data through envelope metadata and job events.
Spec reference: §11.
Envelope includes optional trace_id. Runtimes should copy trace ids from
submit envelopes to job events, terminal outcomes, and delegated children.
Reserved job event kinds include log and metric. Use these for structured
agent telemetry that should travel with the job stream.
ToolContext::charge emits cost.budget.remaining metrics as budget counters
decrease. Consumers can subscribe to those events for live spend dashboards.
The crate carries the protocol data needed for OpenTelemetry integration, but
does not ship a native OTel middleware package. Applications can wrap
transports or runtime handlers and propagate W3C trace context through
Envelope::extensions under a registered extension key (e.g.
arcpx.opentelemetry.tracecontext.v1).
See examples/tracing.rs for trace-id usage.