Constant IDLE_PROBE_BACKOFF_MAX_SECS 

const IDLE_PROBE_BACKOFF_MAX_SECS: u64 = 300;

Ceiling for the idle-probe back-off. Once the probe has failed enough times in a row, we settle at one attempt every five minutes — frequent enough to recover if the windowing-system extension reappears, rare enough that a permanently-missing one (e.g. X11 with no MIT-SCREEN-SAVER) no longer floods stderr with libX11 warnings.