fix(tui): keep sidebar resize live during active turns

The loading mouse filter (should_drop_loading_mouse_motion) dropped all
Drag events while app.is_loading unless a transcript selection or
scrollbar drag was active. A sidebar resize started on the handle
(Down passes the filter) then never received its Drag events, leaving
the resize wedged mid-gesture during live runs (#3063, symptom of the
#3096 subagent-runtime pressure on the TUI).

- Allow Drag events through the loading filter while
  app.sidebar_resizing is set.
- Clear last_sidebar_area / last_sidebar_handle_area and any in-flight
  resize when the sidebar is hidden or doesn't fit, so stale handle
  hit-areas can't capture clicks.
- Tests: resize down/drag/up while loading, mouse-up outside the
  handle still ends the resize.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/tui/src/tui/mouse_ui.rs

@@ -38,8 +38,11 @@ pub(crate) fn should_drop_loading_mouse_motion(app: &App, mouse: MouseEvent) ->
             !(over_sidebar || app.sidebar_hover_tooltip.is_some())
         }
         MouseEventKind::Drag(_) => {
+            // Sidebar drag-to-resize must stay live during active turns —
+            // dropping these events wedges the resize state mid-drag (#3063).
             !app.viewport.transcript_selection.dragging
                 && !app.viewport.transcript_scrollbar_dragging
+                && !app.sidebar_resizing
         }
         _ => false,
     }

crates/tui/src/tui/ui.rs

@@ -7654,6 +7654,15 @@ fn render(f: &mut Frame, app: &mut App) {
         // hit-testing can route scroll events correctly.
         app.viewport.last_sidebar_area = sidebar_area;
 
+        // When the sidebar is hidden or doesn't fit, drop its stale mouse
+        // hit areas and any in-flight resize so clicks on those columns
+        // don't keep routing to an invisible handle (#3063).
+        if sidebar_area.is_none() {
+            app.last_sidebar_area = None;
+            app.last_sidebar_handle_area = None;
+            app.sidebar_resizing = false;
+        }
+
         let chat_widget = ChatWidget::new(app, chat_area);
         let buf = f.buffer_mut();
         chat_widget.render(chat_area, buf);

crates/tui/src/tui/ui/tests.rs

@@ -727,6 +727,53 @@ fn loading_mouse_filter_keeps_active_drags() {
     app.viewport.transcript_selection.dragging = false;
     app.viewport.transcript_scrollbar_dragging = true;
     assert!(!should_drop_loading_mouse_motion(&app, drag));
+
+    // Sidebar drag-to-resize must also survive the loading filter (#3063).
+    app.viewport.transcript_scrollbar_dragging = false;
+    app.sidebar_resizing = true;
+    assert!(!should_drop_loading_mouse_motion(&app, drag));
+}
+
+#[test]
+fn loading_mouse_filter_allows_sidebar_resize_down_drag_up() {
+    let mut app = create_test_app();
+    app.is_loading = true;
+    setup_resize_handle(&mut app, 80, 33, 120);
+
+    let down = MouseEvent {
+        kind: MouseEventKind::Down(MouseButton::Left),
+        column: 80,
+        row: 5,
+        modifiers: KeyModifiers::NONE,
+    };
+    assert!(!should_drop_loading_mouse_motion(&app, down));
+    handle_mouse_event(&mut app, down);
+    assert!(app.sidebar_resizing, "down on handle starts resize");
+
+    let drag = MouseEvent {
+        kind: MouseEventKind::Drag(MouseButton::Left),
+        column: 76,
+        row: 5,
+        modifiers: KeyModifiers::NONE,
+    };
+    assert!(
+        !should_drop_loading_mouse_motion(&app, drag),
+        "resize drag must not be dropped while loading"
+    );
+    handle_mouse_event(&mut app, drag);
+    let expected = ((37u32 * 100) / 120) as u16;
+    assert_eq!(app.sidebar_width_percent, expected);
+
+    let up = MouseEvent {
+        kind: MouseEventKind::Up(MouseButton::Left),
+        column: 76,
+        row: 5,
+        modifiers: KeyModifiers::NONE,
+    };
+    assert!(!should_drop_loading_mouse_motion(&app, up));
+    handle_mouse_event(&mut app, up);
+    assert!(!app.sidebar_resizing);
+    assert!(app.sidebar_width_dirty);
 }
 
 #[test]
@@ -3626,6 +3673,32 @@ fn sidebar_resize_up_ends_resizing_and_marks_dirty() {
     );
 }
 
+#[test]
+fn sidebar_resize_up_outside_handle_still_ends_resizing() {
+    let mut app = create_test_app();
+    setup_resize_handle(&mut app, 80, 33, 120);
+    app.sidebar_resizing = true;
+    app.sidebar_resize_anchor_x = 80;
+    app.sidebar_resize_anchor_width = 33;
+
+    // Release far away from the handle and the sidebar entirely.
+    handle_mouse_event(
+        &mut app,
+        MouseEvent {
+            kind: MouseEventKind::Up(MouseButton::Left),
+            column: 5,
+            row: 20,
+            modifiers: KeyModifiers::NONE,
+        },
+    );
+
+    assert!(
+        !app.sidebar_resizing,
+        "mouse up must clear resize state even outside the handle"
+    );
+    assert!(app.sidebar_width_dirty);
+}
+
 fn make_subagent(
     id: &str,
     status: crate::tools::subagent::SubAgentStatus,