fix(dock): keep auto-hiding panels shown while the pointer is on their dropdowns

iced gives the layer under an overlay a levitating cursor, so the dock
edge's mouse_area read the pointer on any dropdown or combo list in a
pallet as leaving, and auto-hide collapsed the panel mid-pick. Track
enter/leave with a small hover_zone wrapper that lands the cursor before
its bounds test, on docked edges and floating pallets alike.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_014ihuqzxdUhd9UbioPn5MGu

src/app/dock/update.rs

@@ -207,12 +207,12 @@ impl OpenCADStudio {
                         Some(HoverPending::Hide)
                             if self.dock_peek.is_some_and(|id| self.dock.auto_hides(id)) =>
                         {
-                            // A dropdown or the colour window opened from the
-                            // panel draws as an overlay, which the edge's
-                            // mouse area reads as the pointer leaving. Keep
-                            // the panel out until it closes, so a pick can
-                            // still land; then hide unless the pointer is
-                            // back (its re-entry cancels this).
+                            // The edge's hover zone keeps a dropdown inside
+                            // it from reading as a leave; a colour popup can
+                            // still reach past it (or be the Select Color
+                            // window). Keep the panel out until it closes, so
+                            // a pick can still land; then hide unless the
+                            // pointer is back (its re-entry cancels this).
                             if self.dock_popup_open() {
                                 return self.dock_hover_arm(HoverPending::Hide);
                             }

src/app/dock/view.rs

@@ -164,12 +164,13 @@ impl OpenCADStudio {
                 children.push(strip);
             }
         }
-        Some(
-            mouse_area(row(children).height(Fill))
-                .on_enter(Message::Dock(crate::ui::dock::DockMsg::HoverStay))
-                .on_exit(Message::Dock(crate::ui::dock::DockMsg::HoverExit))
-                .into(),
-        )
+        // Not a `mouse_area`: the pointer on one of the pallet's own
+        // dropdowns must not read as leaving the edge.
+        Some(crate::ui::hover_zone::hover_zone(
+            row(children).height(Fill),
+            Message::Dock(crate::ui::dock::DockMsg::HoverStay),
+            Message::Dock(crate::ui::dock::DockMsg::HoverExit),
+        ))
     }
 
     /// An edge's vertical icon strip: per group its open pallets' icons in a
@@ -555,10 +556,14 @@ impl OpenCADStudio {
         // on its empty areas don't fall through to the drawing below.
         let panel = mouse_area(framed)
             .on_press(Message::Dock(DockMsg::FloatRaise(f.id)))
-            .on_enter(Message::Dock(DockMsg::Hover(f.id)))
-            .on_exit(Message::Dock(DockMsg::HoverExit))
             .interaction(iced::mouse::Interaction::Idle);
-        place_at(panel.into(), x, y)
+        // Enter / leave as on a docked edge: its dropdowns keep it shown.
+        let panel = crate::ui::hover_zone::hover_zone(
+            panel,
+            Message::Dock(DockMsg::Hover(f.id)),
+            Message::Dock(DockMsg::HoverExit),
+        );
+        place_at(panel, x, y)
     }
 
     /// Where floating panel `f` draws.