Per-OS detection

Three signals — Do Not Disturb, camera in use, and idle time — are read directly from each operating system. There's no portable abstraction; each platform gets its own implementation.

Matrix

Feature	macOS	Windows	Linux
DnD	~/Library/DoNotDisturb/DB/Assertions.json poll	WNF NtQueryWnfStateData (state 0xA3BC1875_A3BC0875)	not implemented
Camera	log stream event-driven	HKCU\…\ConsentStore\webcam poll (2s)	walk /proc/<pid>/fd/* for /dev/video* (2s)
Idle	user-idle (CGEventSourceSeconds…)	user-idle (GetLastInputInfo)	user-idle X11; Wayland is unreliable

Known rough edges

• Windows DnD WNF state name — 0xA3BC1875_A3BC0875 is empirically derived. If toggling Focus Assist on a Windows build doesn't pause breaks, that constant is the first thing to verify.
• Linux DnD — would need per-DE handling (GNOME gsettings, KDE DBus). The setting checkbox is currently greyed with a (macOS/Windows only) suffix.
• Wayland idle — user-idle's X11 implementation is reliable; Wayland is not. X11-only Linux support is the practical short-term limit.

Activation policy

macOS uses ActivationPolicy::Accessory — no Dock icon, no app menu in the menu bar. The tray icon is the only entry point. The tray uses trayIconTemplate.png as a template image so AppKit auto-tints it for light/dark menu bars. Don't replace it with a coloured PNG.