The cpal stream-error closure used `let _ = err_tx.try_send(...)` against a
bounded sync_channel(16). If the live session's listener stalled or the
frontend disconnected, runtime stream errors were silently dropped — the
diagnostic bundle showed nothing for a session that mysteriously stopped
working.
- Bump the error channel capacity 16 → 32 (matches AUDIO_CHANNEL_CAPACITY).
- On try_send failure, log to stderr with the device name + a per-session
drop counter so the symptom is visible in the diagnostic bundle even
when the typed event never reached the frontend.
- Plumb a new `dropped_errors: Arc<AtomicU64>` through `build_input_stream`
alongside the existing `dropped_chunks`, mirroring the same pattern.
(kon-audio doesn't build in the audit sandbox: it links against ALSA
which the sandbox lacks. CI cross-platform compiles it.)
https://claude.ai/code/session_0189xUb6ie6t9qHkzatGZ9Rb
a7fdc96e7b