Refresh worktree-drag highlights on modifier change and in copy mode

- `should_highlight_background_for_selection_drag` now takes
  `is_copy_mode` and returns false for pure-root drags in copy mode,
  matching the existing per-row highlight logic. The blank-area
  on_drag_move handler reads the modifier and threads it through.
- The on_modifiers_changed listener now also clears the cached drag
  target so the next drag-move event recomputes the highlight under
  the new mode. Without this, the on_drag_move fast path skipped the
  recomputation while the pointer stayed put on the same row.
- Extracted the modifier-changed logic into
  `ProjectPanel::handle_drag_modifiers_changed` so it can be tested
  directly.
- Adds tests for both fixes.

crates/project_panel/src/project_panel.rs

@@ -4467,6 +4467,22 @@ impl ProjectPanel {
         .detach();
     }
 
+    fn handle_drag_modifiers_changed(
+        &mut self,
+        modifiers: &Modifiers,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        self.refresh_drag_cursor_style(modifiers, window, cx);
+        // The copy modifier flips highlight semantics for worktree-root
+        // drags. Drop the cached target so the next drag-move event
+        // recomputes under the new mode — otherwise the on_drag_move
+        // fast path skips the recomputation while the pointer stays put.
+        if self.drag_target_entry.take().is_some() {
+            cx.notify();
+        }
+    }
+
     fn refresh_drag_cursor_style(
         &self,
         modifiers: &Modifiers,
@@ -5342,19 +5358,28 @@ impl ProjectPanel {
         &self,
         drag_state: &DraggedSelection,
         last_root_id: ProjectEntryId,
+        is_copy_mode: bool,
         cx: &App,
     ) -> bool {
+        let project = self.project.read(cx);
+
+        // Worktree roots can't be copied, so a pure-root copy drag is a
+        // guaranteed no-op — don't advertise the background as a target.
+        if is_copy_mode
+            && drag_state
+                .items()
+                .all(|entry| project.entry_is_worktree_root(entry.entry_id, cx))
+        {
+            return false;
+        }
+
         // Always highlight for multiple entries
         if drag_state.items().count() > 1 {
             return true;
         }
 
         // Since root will always have empty relative path
-        if let Some(entry_path) = self
-            .project
-            .read(cx)
-            .path_for_entry(drag_state.active_selection.entry_id, cx)
-        {
+        if let Some(entry_path) = project.path_for_entry(drag_state.active_selection.entry_id, cx) {
             if let Some(parent_path) = entry_path.path.parent() {
                 if !parent_path.is_empty() {
                     return true;
@@ -5363,11 +5388,7 @@ impl ProjectPanel {
         }
 
         // If parent is empty, check if different worktree
-        if let Some(last_root_worktree_id) = self
-            .project
-            .read(cx)
-            .worktree_id_for_entry(last_root_id, cx)
-        {
+        if let Some(last_root_worktree_id) = project.worktree_id_for_entry(last_root_id, cx) {
             if drag_state.active_selection.worktree_id != last_root_worktree_id {
                 return true;
             }
@@ -6751,7 +6772,7 @@ impl Render for ProjectPanel {
                 .relative()
                 .on_modifiers_changed(cx.listener(
                     |this, event: &ModifiersChangedEvent, window, cx| {
-                        this.refresh_drag_cursor_style(&event.modifiers, window, cx);
+                        this.handle_drag_modifiers_changed(&event.modifiers, window, cx);
                     },
                 ))
                 .key_context(self.dispatch_context(window, cx))
@@ -7094,16 +7115,23 @@ impl Render for ProjectPanel {
                                     },
                                 ))
                                 .on_drag_move::<DraggedSelection>(cx.listener(
-                                    move |this, event: &DragMoveEvent<DraggedSelection>, _, cx| {
+                                    move |this,
+                                          event: &DragMoveEvent<DraggedSelection>,
+                                          window,
+                                          cx| {
                                         let Some(last_root_id) = this.state.last_worktree_root_id
                                         else {
                                             return;
                                         };
                                         if event.bounds.contains(&event.event.position) {
                                             let drag_state = event.drag(cx);
+                                            let is_copy_mode = Self::is_copy_modifier_set(
+                                                &window.modifiers(),
+                                            );
                                             if this.should_highlight_background_for_selection_drag(
                                                 &drag_state,
                                                 last_root_id,
+                                                is_copy_mode,
                                                 cx,
                                             ) {
                                                 this.drag_target_entry =

crates/project_panel/src/project_panel_tests.rs

@@ -9480,6 +9480,7 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
         let result = panel.should_highlight_background_for_selection_drag(
             &multiple_dragged_selection,
             root1_entry.id,
+            false,
             cx,
         );
         assert!(result, "Should highlight background for multiple entries");
@@ -9499,6 +9500,7 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
         let result = panel.should_highlight_background_for_selection_drag(
             &nested_dragged_selection,
             root1_entry.id,
+            false,
             cx,
         );
         assert!(result, "Should highlight background for nested file");
@@ -9518,6 +9520,7 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
         let result = panel.should_highlight_background_for_selection_drag(
             &root_file_dragged_selection,
             root1_entry.id,
+            false,
             cx,
         );
         assert!(
@@ -9529,6 +9532,7 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
         let result = panel.should_highlight_background_for_selection_drag(
             &root_file_dragged_selection,
             root2_entry.id,
+            false,
             cx,
         );
         assert!(
@@ -9551,6 +9555,7 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
         let result = panel.should_highlight_background_for_selection_drag(
             &child_file_dragged_selection,
             root1_entry.id,
+            false,
             cx,
         );
         assert!(
@@ -9560,6 +9565,112 @@ async fn test_should_highlight_background_for_selection_drag(cx: &mut gpui::Test
     });
 }
 
+// In copy mode, a pure worktree-root drag is a no-op, so the blank area
+// below the panel should not light up as a valid drop target.
+#[gpui::test]
+async fn test_should_highlight_background_suppressed_for_root_drag_in_copy_mode(
+    cx: &mut gpui::TestAppContext,
+) {
+    init_test(cx);
+
+    let fs = FakeFs::new(cx.executor());
+    fs.insert_tree("/root1", json!({ "a.txt": "" })).await;
+    fs.insert_tree("/root2", json!({ "b.txt": "" })).await;
+
+    let project =
+        Project::test(fs.clone(), ["/root1".as_ref(), "/root2".as_ref()], cx).await;
+    let window = cx.add_window(|window, cx| MultiWorkspace::test_new(project.clone(), window, cx));
+    let workspace = window
+        .read_with(cx, |mw, _| mw.workspace().clone())
+        .unwrap();
+    let cx = &mut VisualTestContext::from_window(window.into(), cx);
+    let panel = workspace.update_in(cx, ProjectPanel::new);
+    cx.run_until_parked();
+
+    panel.update(cx, |panel, cx| {
+        let worktrees: Vec<_> = panel.project.read(cx).visible_worktrees(cx).collect();
+        let r1 = worktrees[0].read(cx);
+        let r2 = worktrees[1].read(cx);
+        let r1_root_id = r1.root_entry().unwrap().id;
+        let r2_root_id = r2.root_entry().unwrap().id;
+
+        let drag = DraggedSelection {
+            active_selection: SelectedEntry {
+                worktree_id: r1.id(),
+                entry_id: r1_root_id,
+            },
+            marked_selections: Arc::new([SelectedEntry {
+                worktree_id: r1.id(),
+                entry_id: r1_root_id,
+            }]),
+        };
+
+        // Sanity: in non-copy mode, the background highlights for a cross-
+        // worktree root drag (so the user can drop at the end).
+        assert!(
+            panel.should_highlight_background_for_selection_drag(
+                &drag,
+                r2_root_id,
+                false,
+                cx,
+            ),
+            "non-copy root drag should highlight background"
+        );
+
+        // In copy mode, the same drag is a no-op → no background highlight.
+        assert!(
+            !panel.should_highlight_background_for_selection_drag(
+                &drag,
+                r2_root_id,
+                true,
+                cx,
+            ),
+            "copy-mode root drag should suppress background highlight"
+        );
+    });
+}
+
+// Toggling the copy modifier while the cursor stays still must invalidate
+// the cached drag target so the next drag-move event recomputes the
+// highlight under the new mode (otherwise the row stays in its old
+// highlight state until the pointer leaves and re-enters).
+#[gpui::test]
+async fn test_modifier_change_clears_drag_target_entry(
+    cx: &mut gpui::TestAppContext,
+) {
+    init_test(cx);
+
+    let fs = FakeFs::new(cx.executor());
+    fs.insert_tree("/root1", json!({ "a.txt": "" })).await;
+
+    let project = Project::test(fs.clone(), ["/root1".as_ref()], cx).await;
+    let window = cx.add_window(|window, cx| MultiWorkspace::test_new(project.clone(), window, cx));
+    let workspace = window
+        .read_with(cx, |mw, _| mw.workspace().clone())
+        .unwrap();
+    let cx = &mut VisualTestContext::from_window(window.into(), cx);
+    let panel = workspace.update_in(cx, ProjectPanel::new);
+    cx.run_until_parked();
+
+    panel.update_in(cx, |panel, window, cx| {
+        panel.drag_target_entry = Some(DragTarget::Background);
+        panel.handle_drag_modifiers_changed(
+            &gpui::Modifiers {
+                alt: true,
+                control: true,
+                ..Default::default()
+            },
+            window,
+            cx,
+        );
+        assert!(
+            panel.drag_target_entry.is_none(),
+            "modifier change should clear drag_target_entry so the next \
+             drag-move can recompute highlights under the new mode"
+        );
+    });
+}
+
 #[gpui::test]
 async fn test_hide_root(cx: &mut gpui::TestAppContext) {
     init_test(cx);