feat: notify when a track stops growing mid-recording

[jayfrid-bot]

Motivation

Companion to #2. That PR fixes the specific way a track can silently die (a call app reconfiguring the input device); this one adds a safety net for the general case — any track that stops being written mid-session, for any reason, should be surfaced to the user during the meeting, not discovered afterward in a one-sided transcript.

What it does

RecordingSession now runs a lightweight liveness watchdog while recording:

• Both .caf files grow continuously while their capture is healthy, so a 15s timer polls their sizes.
• A track frozen for 45s fires a user notification via the existing notifyUser helper: "quill: mic track stalled — no mic audio written for 45s — the recording may be incomplete."
• Growth clears the stall state and announces recovery, so a track that dies, recovers, and dies again alerts both times without spamming in between.

No new dependencies, no work when nothing is wrong (two stat calls per 15s).

Verification

Tested against the real failure mode from #2: a build with the mic auto-restart disabled, recording during a live FaceTime call. The mic track died when the call connected (27s into a 2:01 session) and the stall notification fired within the expected window. Also verified the timer is torn down on stop and that healthy sessions produce no notifications.

🤖 Generated with Claude Code

[sollrr9]

🤖 Grok (xAI) PR Review — model: grok-4.5

verdict: LGTM
tests: not run: swift unavailable on review host (macOS package)
linked_issues: #2 partial: notify only, no capture restart

Issues (must-fix)

• none

Suggestions

• Sources/quill/RecordingSession.swift:124 — also log stall/recovery to session stderr/transcribe path
• Sources/quill/RecordingSession.swift:59 — seed trackLastGrew at start so first stall window is 45s not ~60s

Next steps: merge when green | keep companion #2 for auto-restart