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, 70 insertions, 0 deletions

diff --git a/src/app/actions.rs b/src/app/actions.rs
index b7634c3c..f8ae511f 100644
--- a/src/app/actions.rs
+++ b/src/app/actions.rs
@@ -113,6 +113,8 @@ impl AppState {
 
     pub fn switch_workspace(&mut self, idx: usize) {
         if idx < self.workspaces.len() {
+            self.selection = None;
+            self.selection_autoscroll = None;
             self.active = Some(idx);
             self.selected = idx;
             let workspace_id = self.workspaces[idx].id.clone();
@@ -196,6 +198,8 @@ impl AppState {
 
     pub fn switch_tab(&mut self, idx: usize) {
         if let Some(ws_idx) = self.active {
+            self.selection = None;
+            self.selection_autoscroll = None;
             let Some(ws) = self.workspaces.get_mut(ws_idx) else {
                 return;
             };
@@ -470,6 +474,8 @@ impl AppState {
         if self.workspaces.is_empty() {
             return;
         }
+        self.selection = None;
+        self.selection_autoscroll = None;
         self.mark_session_dirty();
         let terminal_ids = self.terminal_ids_for_workspace(self.selected);
         let workspace_id = self.workspaces[self.selected].id.clone();
@@ -590,6 +596,8 @@ impl AppState {
     }
 
     pub fn close_pane(&mut self) {
+        self.selection = None;
+        self.selection_autoscroll = None;
         self.mark_session_dirty();
         let active = self.active;
         let terminal_ids = active
@@ -615,6 +623,8 @@ impl AppState {
     }
 
     pub fn close_tab(&mut self) {
+        self.selection = None;
+        self.selection_autoscroll = None;
         self.mark_session_dirty();
         let should_close_workspace = self
             .active
@@ -654,6 +664,11 @@ impl AppState {
 impl AppState {
     pub fn clear_selection(&mut self) {
         self.selection = None;
+        self.selection_autoscroll = None;
+    }
+
+    pub(crate) fn stop_selection_autoscroll_state(&mut self) {
+        self.selection_autoscroll = None;
     }
 
     pub fn copy_selection(&mut self) {
@@ -682,6 +697,7 @@ impl AppState {
         }
 
         self.selection = None;
+        self.selection_autoscroll = None;
     }
 }
 
@@ -918,6 +934,15 @@ impl AppState {
             return;
         };
 
+        if self
+            .selection
+            .as_ref()
+            .is_some_and(|s| s.pane_id == pane_id)
+        {
+            self.selection = None;
+            self.selection_autoscroll = None;
+        }
+
         let pane_terminal_id = self.terminal_id_for_pane(ws_idx, pane_id);
         let workspace_terminal_ids = self.terminal_ids_for_workspace(ws_idx);
         let should_close_workspace = {
@@ -1340,6 +1365,51 @@ mod tests {
     }
 
     #[test]
+    fn pane_died_unrelated_pane_preserves_selection() {
+        // Two workspaces; user is selecting text in workspace 0.
+        // A pane in workspace 1 dies — selection must be preserved.
+        let mut state = app_with_workspaces(&["active", "bg"]);
+        let active_pane = *state.workspaces[0].panes.keys().next().unwrap();
+        let bg_pane = *state.workspaces[1].panes.keys().next().unwrap();
+
+        state.selection = Some(crate::selection::Selection::anchor(active_pane, 0, 0, None));
+        state.selection_autoscroll = Some(crate::app::state::SelectionAutoscroll {
+            direction: crate::app::state::SelectionAutoscrollDirection::Down,
+            last_mouse_screen_col: 0,
+            last_mouse_screen_row: 23,
+            inner_rect: ratatui::layout::Rect::new(0, 0, 80, 24),
+        });
+
+        state.handle_pane_died(bg_pane);
+
+        assert!(state.selection.is_some());
+        assert!(state.selection_autoscroll.is_some());
+    }
+
+    #[test]
+    fn pane_died_same_pane_clears_selection() {
+        let mut state = app_with_workspaces(&["test"]);
+        let first_id = state.workspaces[0].tabs[0].root_pane;
+        let second_id = state.workspaces[0].test_split(Direction::Horizontal);
+
+        state.selection = Some(crate::selection::Selection::anchor(second_id, 0, 0, None));
+        state.selection_autoscroll = Some(crate::app::state::SelectionAutoscroll {
+            direction: crate::app::state::SelectionAutoscrollDirection::Down,
+            last_mouse_screen_col: 0,
+            last_mouse_screen_row: 23,
+            inner_rect: ratatui::layout::Rect::new(0, 0, 80, 24),
+        });
+
+        state.handle_pane_died(second_id);
+
+        // first_id still alive, workspace stays, but selection was on the dying pane
+        assert!(state.selection.is_none());
+        assert!(state.selection_autoscroll.is_none());
+        assert_eq!(state.workspaces[0].panes.len(), 1);
+        assert_eq!(state.workspaces[0].panes.keys().next().unwrap(), &first_id);
+    }
+
+    #[test]
     fn state_changed_updates_pane() {
         let mut state = app_with_workspaces(&["test"]);
         let pane_id = *state.workspaces[0].panes.keys().next().unwrap();