Two compounding root causes produced a "PiP-style grey view" briefly visible after Join Voice on mobile:
1. MobileSpacesScreen.handleVoiceJoin pushed 'voice' onto the mobile stack. MobileShell.screenMap only has 'voice-full' — the renderer returned null for 'voice' while the root screen sat under `visibility: hidden` (stack length > 0). Corrected to 'voice-full' with an explanatory comment.
2. AppLayout mounted the desktop <PictureInPicture /> in the mobile branch too. Its visibility check `(isInServerVoice || isInDmCall) && !voiceFullscreen` is true the moment currentVoiceChannelId is set, so the desktop PiP rendered as the only visible UI on top of the hidden mobile shell. Removed from the mobile branch; kept on desktop. Added a comment to prevent regression.
Mobile owns its voice overlay chrome exclusively via MobileVoiceMiniBar + MobileVoiceFullScreen.
Spec: docs/systems/mobile-ui.md gains a "Voice Join Flow (Mobile)" subsection and a leading paragraph in "Voice Overlay" stating that PiP is desktop-only.
Jannis Braun
71b383ce7f