The original fetch_events() call blocked indefinitely on the evdev device.
In VM environments, the grabbed keyboard device may not deliver events
after the initial batch, causing the 30-second safety timeout to trigger
silently — the daemon exits, the grab is released, and subsequent
keystrokes bypass the IME entirely.
Replace with libc::poll() with a 100ms timeout so the event loop stays
responsive. When poll returns 0 (timeout), the loop checks signals, the
30-second grab-safety timeout, and also polls for background window
changes. This ensures the safety timeout actually fires as expected,
and the daemon correctly detects and handles the no-event condition.
Also check for background window class changes during idle periods
(no keypress events) so app detection works consistently.