fix: window state preservation

[mayakwd]

Fixes a bunch of issues where the maximized/snapped state of a window was lost in scenarios involving:

• transitions to full-screen mode,
• from full-screen mode to snapped state,
• moving full-screen/snapped window between workspaces.

Exact fixes:

• For Chromium and similar clients, implements strict protocol compliance via pre-set fullscreen before unmap. Unmap sends intermediate configures considered by Chromium as a refusal to transition to full-screen mode, as they did not contain full-screen. This fixes the issue: [BUG] Maximized chromium browsers: clicking video fullscreen makes browser fullscreen instead #1642 (for both maximized and snapped windows).

• Preserving snapped state when transitioning to fullscreen/minimizing. FloatingRestoreData now stores was_snapped: Option<TiledCorners>. The information is captured before floating_layer.unmap() clears it and is used later for restoration.

• Preserving maximized/snapped state when moving between workspaces. After moving the window, the maximized or snapped state from FloatingRestoreData is re-applied in the target workspace (Maximized windows don't stay maximized when they are moved to a different display or workspace #528, Maximized window loses its state when moved to another workspace cosmic-epoch#2608)

What I tested:

• Maximize Chrome > Click fullscreen on any video > Single-click fullscreen
• Maximize Firefox > Click fullscreen on any video > Single-click fullscreen (regression check)
• Snap Chrome to a corner/side > Click fullscreen on any video > Single-click fullscreen
• Snap window to a corner/side > Go fullscreen > Exit fullscreen > Window returns to the snap position
• Maximize window > Move window to the other workspace > Window stays maximized
• Snap window to a corner/side > Move window to the other workspace > Window stays snapped to the same corner/side

I tried to make the changes as small as possible.

I also wanted to fix the issue with returning the window to the stack from full-screen state in this PR, but it appears to be much more complicated than I initially imagined and has a lot of edge cases.

[Drakulix]

Thanks! These are very welcome and easy to review bugfixes.

I added some comments, as I would like to see some of the new code to be moved around slightly, if you don't mind.

[Drakulix]

Thanks! Code-wise this looks great now. Just needs a QA review.

[rhessus]

@Drakulix There is a small issue with this fix. When I move a maximized window between two workspaces, the destination workspace does not apply the maximized style to the panel and dock, and the source workspace keeps that style instead (opaque/transparent panel and dock). Not sure if that’s very clear…

2026-02-24.19-34-50.mp4

[Milli189]

there is an issue with this pull request, whenever I fullscreen a chromium based browser, then the scrolling stops being smooth and goes back to 60hz, and also when I maximize a chromium based browser or I fullscreen a video and I move the cursor to the top of the monitor to activate the "X" that appears on chromium based browsers to remove the fullscreen, it doesn't always happen and the anymation can be laggy, which doesn't happen on KDE Plasma