fix(tui): clear stale scrollbar drag state

crates/tui/src/tui/app.rs

@@ -2467,6 +2467,7 @@ impl App {
 
         self.viewport.pending_scroll_delta = 0;
         self.viewport.transcript_selection.clear();
+        self.viewport.transcript_scrollbar_dragging = false;
 
         self.viewport.last_transcript_area = None;
         self.viewport.last_transcript_top = 0;

crates/tui/src/tui/ui.rs

@@ -7338,6 +7338,8 @@ fn handle_mouse_event(app: &mut App, mouse: MouseEvent) -> Vec<ViewEvent> {
             }
         }
         MouseEventKind::Down(MouseButton::Left) => {
+            app.viewport.transcript_scrollbar_dragging = false;
+
             if mouse_hits_rect(mouse, app.viewport.jump_to_latest_button_area) {
                 app.scroll_to_bottom();
                 return Vec::new();

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

@@ -359,6 +359,38 @@ fn transcript_scrollbar_drag_maps_mouse_row_to_scroll_position() {
     assert!(!app.viewport.transcript_scrollbar_dragging);
 }
 
+#[test]
+fn new_left_down_clears_stale_transcript_scrollbar_drag() {
+    let mut app = create_test_app();
+    app.history = vec![HistoryCell::Assistant {
+        content: "alpha beta".to_string(),
+        streaming: false,
+    }];
+    app.resync_history_revisions();
+    app.viewport.last_transcript_area = Some(Rect {
+        x: 2,
+        y: 5,
+        width: 20,
+        height: 10,
+    });
+    app.viewport.last_transcript_visible = 10;
+    app.viewport.last_transcript_total = 110;
+    app.viewport.transcript_scrollbar_dragging = true;
+
+    let events = handle_mouse_event(
+        &mut app,
+        MouseEvent {
+            kind: MouseEventKind::Down(MouseButton::Left),
+            column: 3,
+            row: 5,
+            modifiers: KeyModifiers::NONE,
+        },
+    );
+
+    assert!(events.is_empty());
+    assert!(!app.viewport.transcript_scrollbar_dragging);
+}
+
 #[test]
 fn right_click_opens_context_menu() {
     let mut app = create_test_app();