bmux_recording_runtime

Neutral primitive crate hosting the RecordingSink trait + registry handle for the recording-plugin domain. Both packages/server (core hot-path recording writes) and the recording plugin depend on this crate.

The concrete RecordingRuntime type (with file I/O, rolling windows, etc.) lives in the recording plugin impl crate (bmux_recording_plugin); this crate hosts only the trait abstraction over the write sink plus shared metadata types core needs to construct payloads.