- scripts/headroom-sidecar.py: Unix socket server (from headroom import compress)
- cost.rs: HeadroomSidecar struct with connect/compress methods
- session.rs: build_prompt_messages() now accepts optional sidecar
- daemon.rs: spawns sidecar on startup if COLIBRI_HEADROOM_ENABLED=true
- config.rs: headroom_enabled + headroom_socket_path config fields
- socket.rs: cmd_status reports headroom status, cmd_get_session uses sidecar
- All test fixtures updated with new DaemonConfig fields
40-50% token savings on tool outputs with zero accuracy loss.
Disabled by default (COLIBRI_HEADROOM_ENABLED=false).
Works identically on Linux and FreeBSD.