observability.md scoped the whole feature to Claude Code statistics, so a
reader asking what leaves an agent container would have concluded
counters and nothing else.
That page also documents the trust properties of the agent->collector
hop, and those are what needs restating for a richer payload: same
destination, same credential, same already-accepted ability to push
arbitrary OTLP. What changes is how much detail leaves by default.
docs/swarm/services.md needs no change. It already said each hive ships
the journals of "the harness units inside every agent container" — which
was not true until now.
Part of #3940.
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