Add automatic distributed tracing across coding agents

[Stephen Belanger (Qard)]

Summary

• capture PID/start-time ancestry automatically at daemon IPC ingress and correlate child sessions to active parent tool spans
• support Claude Code, Codex, Pi, and OpenCode through the shared translator span contract, including arbitrary mixed hierarchies and concurrent-agent disambiguation
• use hashed input/output fingerprints only when process ancestry leaves multiple active candidates; ambiguity fails safe without guessing
• persist pending links and compact active-parent snapshots so linkage survives daemon restarts, with dirty-transition handling that prevents stale tool resurrection
• keep capture metadata credential-free and avoid command-line, environment, working-directory, raw prompt, and raw tool-I/O data in active-parent snapshots

Validation

• cargo clippy --manifest-path bt-daemon/Cargo.toml --all-features --all-targets -- -D warnings
• cargo test --locked --manifest-path bt-daemon/Cargo.toml --all-features
• make test
• git diff --check

The distributed integration suite covers all 16 parent/child agent combinations, mixed four-level recursion, concurrent sessions and fan-out, input/output hash disambiguation, daemon restart recovery at every spawn boundary, PID reuse, corrupt/interrupted snapshots, completion cleanup, privacy, and idle retirement.

Deliberate limitation

Remote, container, and remote-MCP children without shared process ancestry currently fail safe as standalone traces. An opaque out-of-band propagation channel is future work.

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[Abhijeet Prasad (AbhiPrasad)]

can you share some example traces of what this looks like?

[Stephen Belanger (Qard)]

Abhijeet Prasad (@AbhiPrasad) https://www.braintrust.dev/app/Braintrust%20SDKs/p/distributed-tracing-test/trace?object_type=project_logs&object_id=d010dc4b-b4f2-421e-a165-232a8e6f062f&r=5b4a249d-86b0-50ac-a831-ac4fa144389b&s=5b4a249d-86b0-50ac-a831-ac4fa144389b