fix: reconcile focus-follows-cursor after workspace switch

[chris-010]

With "focus follows cursor" enabled, switching workspaces left keyboard focus on the newly-active workspace's previously-active window instead of the window under the pointer. Neither holding the pointer still nor moving it within that window corrected it — only a click did.

Focus-follows-cursor is implemented solely as an edge-triggered pointer motion handler that compares the element under the old vs. new pointer position. A workspace switch moves focus without any pointer motion, so the handler never runs, and the switch actions only call Shell::activate(). A click works because the button handler is level-triggered.

This adds State::reconcile_focus_to_pointer(), invoked from the four workspace-switch actions (Workspace, LastWorkspace, NextWorkspace, PreviousWorkspace) on success. When focus-follows-cursor is enabled and the pointer is ungrabbed, it focuses the window under the pointer on the destination workspace, and leaves focus untouched when the pointer is over empty space. MoveToWorkspace/SendToWorkspace are deliberately left alone — the moved window should follow and stay focused.

Fixes: pop-os/cosmic-epoch#3650

Tested on real hardware (Pop!_OS 24.04, COSMIC, Wayland, ThinkPad T490) and in continuous daily use since 2026-07-15.

Why it queries the destination workspace directly, how this relates to #1366 and #2396, and the test runs

It queries the destination workspace's layout directly via Workspace::toplevel_element_under rather than State::element_under: the switch animation is still in progress when the action handler runs, and element_under honours the animation offset, so it would resolve the pointer to the outgoing workspace's window, which Common::refresh_focus then reverts. The full reasoning is in the commit message.

Related issues

• More intuitive cursor behavior for focus_follows_cursor when switching workspaces #1366 asks for exactly this behaviour: "the window under the cursor at the time of switching focus should become the focused window." That is what this implements. The second option offered there — warping the cursor to the last focused window — is not implemented; a plain workspace switch performs no cursor warp.
• [BUG] Mouse hover dead after workspace switch + click switches to wrong workspace #2396 is not claimed to be fixed by this. It reports dead pointer hover after a switch plus clicks landing on the wrong workspace, and its reporter states that toggling focus-follows-cursor made no difference. This change only runs when focus_follows_cursor is enabled and touches neither pointer-motion delivery nor click routing.

Test runs, with the patched build installed as /usr/bin/cosmic-comp:

• Pointer held still over the left tile, switching to a workspace whose last-focused window is the right tile → focus lands on the window under the pointer.
• Hover the right tile, switch away, move the pointer left, switch back → focus lands on the left tile.
• Super+Ctrl+Up/Down (NextWorkspace/PreviousWorkspace) → focus follows the pointer.
• Pointer over empty space → focus is left untouched.
• Verified with cursor_follows_focus both disabled and enabled; a plain workspace switch performs no cursor warp.

On the base, precisely. That runtime testing was done on a build of bb584aa, the commit the installed package is built from. For this PR the change was rebased onto master (f97a852), where it applies cleanly and cargo check --release completes without warnings; the runtime checks above were not repeated on that newer base.

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