[LinuxBoy-96]

cosmic-session blocks logind's power key handling for the whole session, and cosmic-comp handles the key. While cosmic-comp is frozen, the power button does nothing, so a hard reset is the only way out.

cosmic-session now sends a heartbeat every 2 s, one at a time. When cosmic-comp doesn't answer for 10 s, the inhibitor is closed, so a short press of the power button does a clean poweroff through logind. It's taken again as soon as cosmic-comp answers. A cosmic-comp that never answers (an older version) keeps the inhibitor and only gets one message.

Needs pop-os/cosmic-comp#. Related: pop-os/cosmic-comp#, which aborts cosmic-comp after 60 s frozen.

Tested with cosmic-comp nested in Xvfb and a fake logind: with the main thread held for 30 s, the inhibitor was closed after 10 s and taken again as soon as cosmic-comp answered.

Needs pop-os/cosmic-comp#3045. Related: pop-os/cosmic-comp#3044, which aborts cosmic-comp after 60 s frozen.

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