Bug 498235

SUMMARY

It is possible for a window to become unretrievable from any screen.  It can be solected, pressing `ALT F3` brings up the window menu *from the bottom of the screen* but saying to move it, maximize it, fullscreen it, you name it— the window is never visible.  The window stays missing from all screens and activities.

STEPS TO REPRODUCE
1. This is a really weird one and i'm not sure how it happened so you get a story, sorry.  Using two external monitors and the laptop monitor.  So i had enabled the "Center snap zone" in Window Behavior because i was trying to see if, whatever that was, maybe it [would give a way to reset an individual window to snapping to one-half the screen size](https://discuss.kde.org/t/how-do-i-force-meta-arrow-to-resize-window-50-of-screen-width/26171)
2. Step 1 may or may not be related to anything, but as part of trying to make the "center snap zone" do anything at one point a dragged the window by its title bar toward the bottom of the screen… and it disappeared. 
3. When trying to reproduce this i had to drag several times to make it disappear but it never disappeared as fully— i was able to drag it to another monitor screen and start seeing it by using the toggle overview shortcut (Meta+W) and dragging it.  The original window that disappeared does not switch monitors when dragged.

OBSERVED RESULT

The window can be seen in the overview or alt tab and its window menu can be seen with ALT+F3 but the window itself cannot be made to be shown.  Suddenly realizing this is the same experience with the much more serious/reproducible bug #479694

EXPECTED RESULT

There should be no way to drag a window entirely off-screen.

And if it is, moving the window, snapping the window, full-screening the window… something makes it visible again.

SOFTWARE/OS VERSIONS

Operating System: NixOS 25.05
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.9.0
Qt Version: 6.8.1
Kernel Version: 6.6.64 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 9 7940HS w/ Radeon 780M Graphics
Memory: 92.1 GiB of RAM
Graphics Processor: AMD Radeon 780M

ADDITIONAL INFORMATION

I'm sorry.  I hate to file this kind of super-hard-to-reproduce bug, but maybe "simply" making it so windows cannot be entirely dragged offscreen no matter how hard a fool like me might try will be enough to protect others from this.  Thanks!