D: the four independent `= 256` broadcast-channel constants (session events,
local event bus, PTY fan-out, registry events) now derive from one shared
`maestro_config::BroadcastTuning::DEFAULT`, so the coincidence is explicit and
there's a home for per-deployment tuning later.
E: `kill()` and `reap_dead_session()` hand-rolled the same FIFO/sidecar/
worktree/broadcast teardown, differing only in whether tmux still had a session
to kill. Extracted into `cleanup_record(inner, id, record, kill_tmux)`. kill's
sidecar-delete is now best-effort (the session is already out of the
authoritative map), matching the reaper.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>