Add Muse Code hook tracing

[Stephen Belanger (Qard)]

Summary

• Register a first-class muse daemon translator for Muse Code 1.1 hook payloads.
• Configure Muse through a Braintrust-owned managed hook file without merging user hooks.
• Add Muse command definitions for the embedding bt CLI's enable, disable, doctor, and import surfaces.
• Import completed local Muse sessions through export-v1 and the same production translator used by live hooks.
• Support bt trace import muse --all by enumerating durable session IDs through Muse's read-only MSP session/list API before exporting each session.

Behavior and fidelity

bt trace import muse SESSION_ID invokes muse export --session, imports the staged export through the normal delivery pipeline, and removes the temporary export after import. The export reader uses stable session/run/request identifiers and native timestamps, restores complete committed assistant output, and preserves token metrics.

Persistent live hooks remain a low-latency transport. Export-v1 is the authoritative historical fallback when hook output is incomplete. --all does not resume sessions, obtain writer leases, or subscribe to views.

The following are deliberately not exposed yet:

• --attach, because it needs a durable MSP subscription and cursor-following implementation.
• bt trace run muse, because Muse currently has no safe ephemeral configuration overlay; cloning user configuration would be unsafe and could conflict with existing managed hooks.
• Full tool and subagent reconstruction from export-v1, pending a fixture that exercises those native records.

The embedding bt repository must update its embedded daemon revision before the public CLI exposes the new Muse commands.

Validation

• cargo fmt --manifest-path bt-daemon/Cargo.toml -- --check
• cargo clippy --manifest-path bt-daemon/Cargo.toml --all-features --locked -- -D warnings
• cargo test --manifest-path bt-daemon/Cargo.toml --all-features --locked
• A real Muse 1.1.1 echo session imported through the standalone daemon into an isolated debug sink: session root, turn, LLM output, and token metrics were emitted.
• A real import muse --all run enumerated and imported all three durable local Muse sessions through MSP.

The suite passed: 123 unit tests and enabled integration suites. Existing real-agent tests for Codex, Claude, OpenCode, and Pi remain ignored by their own prerequisite checks.