Cut idle CPU from ~15% to ~0%

[spitfiresb]

The problem

The notch was burning 11–19% CPU sitting completely idle, with a matching hit to battery life. Sampling the running process found five always-on loops doing work nobody could see:

1. A system-wide CoreAudio tap ran 24/7 from launch. audioMeter.start() was called unconditionally, so a realtime IO thread filtered every audio sample through six biquads forever — even with nothing playing and the notch collapsed. It also kept the audio stack from power-idling, which is the real battery cost.
2. A now-playing poll fired a synchronous AppleScript round-trip to Spotify every 3s on the main thread. MediaRemote is locked down on recent macOS, so the Spotify fallback path ran constantly — ~3% CPU on its own.
3. The 60 Hz meter tick reassigned @Published bars unconditionally, so silence still invalidated and re-rendered the whole notch 60 times a second.
4. A 16 Hz hover poll read the cursor position forever, whether or not the mouse moved.
5. A 0.15s window-list poll hit WindowServer 6.7×/sec to detect Mission Control.

The fix

• Audio tap follows playback. Starts on play, torn down 2s after pause (delay keeps track-skips from churning CoreAudio device setup). Bars freeze when paused anyway, so nothing is lost visually.
• Spotify updates are event-driven. Listen for PlaybackStateChanged instead of polling; a 15s poll stays as a recovery net.
• Publish only on change. The meter tick skips the assignment when no bar has visibly moved, so silence stops driving renders.
• Hover is event-driven. Mouse-moved monitors replace the poll, plus a 0.5s safety tick for toast-expiry edge cases.
• Overlay poll slowed 0.15s → 0.4s; the existing occlusion notification remains the fast path for detecting Mission Control opening.
• Fallback wiggle capped at 30fps instead of running at 120 Hz display refresh.

Results

Measured on the running app with ps/sample:

Build	Idle CPU
Before	~11–19% sustained
After audio + render + poll fixes	~3%
After event-driven Spotify	~0.9% avg, ~0% at true idle

A 10-second sample of the final build catches essentially nothing on-CPU — no AudioMeter.process, no SpotifyBridge, no renderer frames. Behavior is unchanged: play/pause and track changes still update instantly, and the bars spin up on play.

🤖 Generated with Claude Code

https://claude.ai/code/session_01V66hekkNTU1kraQvcYMZjN