Steam Deck appears to enter sleep but does not after using desktop mode

[Fruktus]

Your system information

• Steam client version: 1721173382
• SteamOS version: 3.5.19
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

I have recently noticed that in some cases after putting my Steam Deck to sleep while in gaming mode after I was using desktop mode it would appear as though it was sleeping but in reality only its screen would be off.
Additionally, at these times the fans wouldn't work (which I believe might be related to #1531) and sometimes it would be unresponsive to anything but forceful shutdown.
I believe that this is caused by processes which normally prevent sleep, but they don't seem to behave correctly while the steam deck is in gaming mode.

I think that this is a relatively serious issue, since the Steam Deck was at these times very hot and if it was for example in bag I believe it could lead to damage to Deck or worse.

One of the possible solutions to this problem is to make it visible that the steam deck failed to enter sleep (maybe by keeping the screen on).

Steps for reproducing this issue:

I have done some debugging and this issue seems to be related to sleep-inhibiting processes.
When such process was active and I pressed the sleep button, the steam deck's screen went black briefly and quickly returned back to desktop which had shown a prompt that something prevented sleep.

However when such process was active and I entered gaming mode and repeated the above the screen would turn black and stay this way, but I was able to ssh into deck and confirm that it is still running.

I've also noticed similar behavior when I've restarted steam deck from ssh console, but I wasn't able to pinpoint what prevented sleep

1. Enter desktop mode
2. Run some sleep-inhibiting process, for example using systemd-inhibit
3. (You can try entering sleep mode via power button and observe that it is aborted)
4. While the sleep-inhibiting process is active, switch to gaming mode
5. Enter sleep mode via power button - the steam deck's screen becomes black and it appears to be sleeping
6. (Verify via ssh that the steam deck is in fact still active)

Performing forceful shutdown and only using gaming mode eliminates this issue.

[Sunspark-007]

Suggestion for an easier method of testing.. wired optical mouse with a red LED for tracking.. if the deck is asleep, the LED will turn off.