fix: prevent idle sleep during playback

README.md

@@ -51,6 +51,8 @@ Compact mode keeps playback in the same floating window; drag to move it and dou
 
 Playback controls stay anchored at the bottom center of the video and cannot be dragged.
 
+Active playback prevents idle system sleep. Local video also keeps the display awake; audio-only playback allows display sleep. Pause, end, close, playback failure and quit release sleep prevention.
+
 ### YouTube
 
 Playback defaults to the best available SDR resolution up to **1080p**. Use **gear → Quality** to select another available resolution, including 4K, or enable automatic quality (off by default). **Show Buffer Info** displays the retained network buffer.
@@ -59,7 +61,7 @@ Only individual videos are supported, not playlists or channels. Private, age-re
 
 ### Chromecast
 
-Open media, select the **Cast** icon or **Playback → Cast to Device → Find Cast Devices…**, and choose a receiver on the same LAN. Allow macOS Local Network access and incoming firewall connections. Keep the Mac awake and connected: it relays the media to the receiver.
+Open media, select the **Cast** icon or **Playback → Cast to Device → Find Cast Devices…**, and choose a receiver on the same LAN. Allow macOS Local Network access and incoming firewall connections. Terebi keeps the Mac awake during the handoff and active Cast playback while allowing the screensaver and display sleep once local playback stops. Keep the Mac connected: it relays media to the receiver. Closing the lid, explicitly sleeping the Mac or critical-battery sleep can still interrupt playback.
 
 Existing controls operate remote playback. **Play on This Mac** returns to local playback at the receiver's position. Opening different media ends casting. Frame stepping and YouTube quality changes are local-only; live Cast playback is not seekable. Cast output is limited to 1080p/30 fps. The screen-and-triangle icon does not provide AirPlay support.