Fix multi-selected desktop icons only ever dragging one at a time

Reported live: "try move desktop items all at once somewhere else"
didn't work. Two compounding bugs, both real: CompState::
desktop_icon_drag only ever tracked one icon id, and the click handler
that starts a drag unconditionally collapsed any existing multi-
selection down to just the grabbed icon before the drag even began.

desktop_icon_drag is now Option<DesktopIconDrag> (crates/wayland/src/
desktop_icons.rs, new type): a grab offset, the grabbed icon's own live
position, and a members list - every currently-selected icon (the
grabbed one included), each a fixed offset from the grabbed icon's own
top-left at drag start, so the group moves as one rigid unit.
input/pointer.rs's click handler now only resets to single-selection
when the grabbed icon isn't already part of the current selection --
grabbing one inside an existing multi-selection keeps the whole group
selected and dragging, matching Windows/GNOME/macOS/KDE convention.
end_desktop_icon_drag snaps every dragged icon to its own nearest free
grid cell independently, tracking newly-claimed cells across the group
so two icons landing near each other never claim the same one.

Full workspace build/test/clippy clean, built and installed. Not unit-
testable (this module has no CompState test fixture for its own
selection/drag logic, an already-documented, accepted gap) - needs a
live drag to confirm.

1 files changed, 14 insertions, 1 deletions

diff --git a/crates/wayland/src/input/pointer.rs b/crates/wayland/src/input/pointer.rs
index 602f613..44b0bd7 100644
--- a/crates/wayland/src/input/pointer.rs
+++ b/crates/wayland/src/input/pointer.rs
@@ -663,7 +663,20 @@ pub(crate) fn handle_pointer_button(state: &mut CompState, pos: Point<f64, Logic
                             state.select_desktop_icon(Some(&id));
                             state.open_desktop_icon(&id);
                         } else {
-                            state.select_desktop_icon(Some(&id));
+                            // Don't collapse an existing multi-selection
+                            // just because the drag grabbed one of its own
+                            // members - `start_desktop_icon_drag` itself
+                            // carries every currently-selected icon along
+                            // when the one grabbed is already selected
+                            // (see its own doc comment), the same "drag one
+                            // of several selected files, they all move"
+                            // convention every real desktop uses. Grabbing
+                            // an icon *outside* the current selection still
+                            // replaces it, same as before.
+                            let already_selected = state.desktop_icons.as_ref().is_some_and(|icons| icons.icons.iter().any(|i| i.id == id && i.selected));
+                            if !already_selected {
+                                state.select_desktop_icon(Some(&id));
+                            }
                             state.start_desktop_icon_drag(&id, origin, (pos.x as i32, pos.y as i32));
                         }
                     }