When the kernel's evdev buffer overflows it sends SYN_DROPPED to signal lost events. Without handling this, a missed key-release can leave key_pressed_devices in a stale state, causing stuck push-to-talk. Discard all events between SYN_DROPPED and the next SYN_REPORT, then reset modifier key state for the affected device. Refs: https://www.kernel.org/doc/html/latest/input/event-codes.html