Per-bot orchestrator: isAvailable() gates on config.enabled + platform +
binary presence; ensureStarted() starts the backend once (idempotent, retries
on failure); playTrack/pause/resume/seek/stop delegate; getPcmStream() proxies
the backend PCM; re-emits backend trackEnded/metadata. backendFactory injected
for tests (fake backend, no real binary/network).
Correction C3: the controller does not re-emit a raw "error" event (Node's
EventEmitter throws on an unhandled "error"); it logs the backend error and
marks itself not-ready so the next ensureStarted() relaunches. getPcmStream()
returns the backend's single persistent stream (no per-attach PassThrough).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>