feat: add selection autoscroll and fix stale selection on transitions (#129)

When dragging to select text near pane edges, a 30ms recurring tick
now continues scrolling and extending the selection while the mouse
is idle. The autoscroll stops on MouseUp, key input, navigate action,
cursor leaving the hot zone, scrollback boundary, missing metrics,
or pane rect change.

Also fixes pre-existing bugs where workspace/tab/pane transitions
failed to clear selection state, which could cause stale selections
to persist across views. Selection clearing on pane death is scoped
to only the dying pane.

Also fixes anchor_screen_pos returning pane-relative coordinates
instead of screen coordinates, which caused false drag detection
and spurious edge autoscroll on same-cell events when the pane
has a non-zero origin.

refs #128

Co-authored-by: leeanh <mac@macs-MacBook-Pro.local>

1 files changed, 49 insertions, 0 deletions

diff --git a/src/app/mod.rs b/src/app/mod.rs
index 1c818a9c..13b8ecc0 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -29,6 +29,7 @@ const MIN_RENDER_INTERVAL: Duration = Duration::from_millis(16);
 pub(crate) const ANIMATION_INTERVAL: Duration = Duration::from_millis(16);
 pub(crate) const HEADLESS_ANIMATION_INTERVAL: Duration = Duration::from_millis(128);
 pub(crate) const HEADLESS_ANIMATION_TICK_STEP: u32 = 8;
+pub(crate) const SELECTION_AUTOSCROLL_INTERVAL: Duration = Duration::from_millis(30);
 const RESIZE_POLL_INTERVAL: Duration = Duration::from_millis(100);
 const GIT_REMOTE_STATUS_REFRESH_INTERVAL: Duration = Duration::from_millis(1500);
 const AUTO_UPDATE_CHECK_INTERVAL: Duration = Duration::from_secs(30 * 60);
@@ -77,6 +78,7 @@ pub struct App {
     pub(crate) next_resize_poll: Instant,
     pub(crate) next_animation_tick: Option<Instant>,
     pub(crate) next_auto_update_check: Option<Instant>,
+    pub(crate) selection_autoscroll_deadline: Option<Instant>,
     pub(crate) session_save_deadline: Option<Instant>,
     pub(crate) last_render_at: Option<Instant>,
     pub(crate) suppressed_repeat_keys:
@@ -363,6 +365,7 @@ impl App {
             workspace_press: None,
             tab_press: None,
             selection: None,
+            selection_autoscroll: None,
             context_menu: None,
             update_available,
             update_install_command,
@@ -451,6 +454,7 @@ impl App {
             next_auto_update_check: auto_updates_enabled(no_session)
                 .then_some(Instant::now() + AUTO_UPDATE_CHECK_INTERVAL),
             session_save_deadline: None,
+            selection_autoscroll_deadline: None,
             last_render_at: None,
             suppressed_repeat_keys: HashSet::new(),
             api_rx,
@@ -2043,6 +2047,51 @@ mod tests {
         assert!(app.session_save_deadline.is_none());
     }
 
+    #[test]
+    fn next_loop_deadline_includes_selection_autoscroll_deadline() {
+        let mut app = test_app();
+        let now = Instant::now();
+        app.selection_autoscroll_deadline = Some(now + Duration::from_millis(5));
+        app.next_animation_tick = Some(now + Duration::from_millis(100));
+        app.session_save_deadline = Some(now + Duration::from_millis(200));
+        assert_eq!(
+            app.next_loop_deadline(now, false),
+            app.selection_autoscroll_deadline
+        );
+    }
+
+    #[test]
+    fn tick_selection_autoscroll_self_heals_when_state_cleared() {
+        let mut app = test_app();
+        let now = Instant::now();
+        app.state.selection_autoscroll = None;
+        app.selection_autoscroll_deadline = Some(now);
+        app.tick_selection_autoscroll(now);
+        assert!(app.selection_autoscroll_deadline.is_none());
+    }
+
+    #[test]
+    fn tick_selection_autoscroll_stops_on_rect_change() {
+        let mut app = test_app();
+        let now = Instant::now();
+        let ws = Workspace::test_new("test");
+        let pane_id = ws.tabs[0].root_pane;
+        app.state.workspaces.push(ws);
+        app.state.active = Some(0);
+        app.state.selection = Some(crate::selection::Selection::anchor(pane_id, 0, 0, None));
+        // Set autoscroll with a stale inner_rect that doesn't match pane_infos
+        app.state.selection_autoscroll = Some(state::SelectionAutoscroll {
+            direction: state::SelectionAutoscrollDirection::Down,
+            last_mouse_screen_col: 0,
+            last_mouse_screen_row: 999,
+            inner_rect: ratatui::layout::Rect::new(0, 0, 1, 1), // wrong rect
+        });
+        app.selection_autoscroll_deadline = Some(now);
+        app.tick_selection_autoscroll(now);
+        assert!(app.state.selection_autoscroll.is_none());
+        assert!(app.selection_autoscroll_deadline.is_none());
+    }
+
     #[tokio::test]
     async fn full_internal_event_queue_eventually_applies_working_to_idle_transition() {
         let mut app = test_app();