fix: add configurable pane gaps

refs #271

7 files changed, 181 insertions, 34 deletions

diff --git a/src/app/agent_resume.rs b/src/app/agent_resume.rs
index 6a24487f..408f5983 100644
--- a/src/app/agent_resume.rs
+++ b/src/app/agent_resume.rs
@@ -1,10 +1,7 @@
 use std::time::Instant;
 
 use bytes::Bytes;
-use ratatui::{
-    layout::Rect,
-    widgets::{Block, Borders},
-};
+use ratatui::layout::Rect;
 
 use super::App;
 
@@ -128,7 +125,12 @@ impl App {
         tab: &crate::workspace::Tab,
         terminal_area: Rect,
     ) -> Vec<crate::layout::PaneInfo> {
-        let mut pane_infos = derived_pending_agent_resume_pane_infos(tab, terminal_area);
+        let mut pane_infos = derived_pending_agent_resume_pane_infos(
+            tab,
+            terminal_area,
+            self.state.pane_borders,
+            self.state.pane_gaps,
+        );
 
         if self.state.active == Some(ws_idx)
             && self
@@ -285,17 +287,13 @@ impl App {
 fn derived_pending_agent_resume_pane_infos(
     tab: &crate::workspace::Tab,
     terminal_area: Rect,
+    pane_borders: bool,
+    pane_gaps: bool,
 ) -> Vec<crate::layout::PaneInfo> {
-    let multi_pane = tab.layout.pane_count() > 1;
-    tab.layout
-        .panes(terminal_area)
+    crate::ui::apply_pane_chrome(tab.layout.panes(terminal_area), pane_borders, pane_gaps)
         .into_iter()
         .map(|mut info| {
-            let pane_inner = if multi_pane {
-                Block::default().borders(Borders::ALL).inner(info.rect)
-            } else {
-                terminal_area
-            };
+            let pane_inner = crate::ui::pane_inner_rect(info.rect, info.borders);
             info.inner_rect = stable_terminal_inner_rect(pane_inner);
             info
         })
@@ -619,6 +617,7 @@ mod tests {
             rect: ratatui::layout::Rect::new(0, 0, 100, 30),
             inner_rect: ratatui::layout::Rect::new(1, 1, 98, 28),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::ALL,
             is_focused: true,
         }];
         app.state.view.terminal_area = ratatui::layout::Rect::new(0, 0, 100, 30);
@@ -735,6 +734,7 @@ mod tests {
             rect: ratatui::layout::Rect::new(0, 0, 100, 30),
             inner_rect: ratatui::layout::Rect::new(1, 1, 98, 28),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::ALL,
             is_focused: true,
         }];
         app.state.view.terminal_area = ratatui::layout::Rect::new(0, 0, 100, 30);
diff --git a/src/app/api/panes.rs b/src/app/api/panes.rs
index 08a9b677..983db238 100644
--- a/src/app/api/panes.rs
+++ b/src/app/api/panes.rs
@@ -1622,18 +1622,20 @@ impl App {
         let tab = ws.tabs.get(tab_idx)?;
         let area = self.state.view.terminal_area;
         let focused_pane_id = self.public_pane_id(ws_idx, tab.layout.focused())?;
-        let panes = tab
-            .layout
-            .panes(area)
-            .into_iter()
-            .filter_map(|pane| {
-                Some(PaneLayoutPane {
-                    pane_id: self.public_pane_id(ws_idx, pane.id)?,
-                    focused: pane.is_focused,
-                    rect: pane.rect.into(),
-                })
+        let panes = crate::ui::apply_pane_chrome(
+            tab.layout.panes(area),
+            self.state.pane_borders,
+            self.state.pane_gaps,
+        )
+        .into_iter()
+        .filter_map(|pane| {
+            Some(PaneLayoutPane {
+                pane_id: self.public_pane_id(ws_idx, pane.id)?,
+                focused: pane.is_focused,
+                rect: pane.rect.into(),
             })
-            .collect();
+        })
+        .collect();
         let splits = tab
             .layout
             .splits(area)
diff --git a/src/app/input/mouse.rs b/src/app/input/mouse.rs
index 41bb5267..c8a03674 100644
--- a/src/app/input/mouse.rs
+++ b/src/app/input/mouse.rs
@@ -393,11 +393,16 @@ impl AppState {
 
                 if !in_sidebar {
                     if let Some(border) = self.find_border_at(mouse.column, mouse.row) {
+                        let grab_offset = match border.direction {
+                            Direction::Horizontal => border.pos.saturating_sub(mouse.column),
+                            Direction::Vertical => border.pos.saturating_sub(mouse.row),
+                        };
                         self.drag = Some(DragState {
                             target: DragTarget::PaneSplit {
                                 path: border.path.clone(),
                                 direction: border.direction,
                                 area: border.area,
+                                grab_offset,
                             },
                         });
                         return None;
@@ -694,14 +699,23 @@ impl AppState {
                             path,
                             direction,
                             area,
+                            grab_offset,
                         } => {
                             let ratio = match direction {
                                 Direction::Horizontal => {
-                                    (mouse.column.saturating_sub(area.x)) as f32
+                                    (mouse
+                                        .column
+                                        .saturating_add(*grab_offset)
+                                        .saturating_sub(area.x))
+                                        as f32
                                         / area.width.max(1) as f32
                                 }
                                 Direction::Vertical => {
-                                    (mouse.row.saturating_sub(area.y)) as f32
+                                    (mouse
+                                        .row
+                                        .saturating_add(*grab_offset)
+                                        .saturating_sub(area.y))
+                                        as f32
                                         / area.height.max(1) as f32
                                 }
                             };
@@ -1257,18 +1271,39 @@ impl AppState {
 
     pub(super) fn find_border_at(&self, col: u16, row: u16) -> Option<&SplitBorder> {
         self.view.split_borders.iter().find(|b| match b.direction {
-            Direction::Horizontal => {
-                col >= b.pos.saturating_sub(1)
+            Direction::Horizontal if self.pane_borders && !self.pane_gaps => {
+                col == b.pos && row >= b.area.y && row < b.area.y + b.area.height
+            }
+            Direction::Horizontal if self.pane_borders && self.pane_gaps => {
+                row >= b.area.y
+                    && row < b.area.y + b.area.height
+                    && col >= b.pos.saturating_sub(1)
                     && col <= b.pos
-                    && row >= b.area.y
+            }
+            Direction::Horizontal if !self.pane_borders && self.pane_gaps => {
+                row >= b.area.y
                     && row < b.area.y + b.area.height
+                    && b.pos.checked_sub(1).is_some_and(|gap_col| {
+                        col == gap_col && self.pane_frame_at(col, row).is_none()
+                    })
+            }
+            Direction::Vertical if self.pane_borders && !self.pane_gaps => {
+                row == b.pos && col >= b.area.x && col < b.area.x + b.area.width
             }
-            Direction::Vertical => {
-                row >= b.pos.saturating_sub(1)
+            Direction::Vertical if self.pane_borders && self.pane_gaps => {
+                col >= b.area.x
+                    && col < b.area.x + b.area.width
+                    && row >= b.pos.saturating_sub(1)
                     && row <= b.pos
-                    && col >= b.area.x
+            }
+            Direction::Vertical if !self.pane_borders && self.pane_gaps => {
+                col >= b.area.x
                     && col < b.area.x + b.area.width
+                    && b.pos.checked_sub(1).is_some_and(|gap_row| {
+                        row == gap_row && self.pane_frame_at(col, row).is_none()
+                    })
             }
+            _ => false,
         })
     }
 
@@ -2612,6 +2647,7 @@ mod tests {
         app.state.workspaces = vec![Workspace::test_new("test")];
         app.state.active = Some(0);
         app.state.selected = 0;
+        app.state.pane_gaps = false;
         app.state.workspaces[0].test_split(Direction::Horizontal);
         crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 106, 20));
         let border = app.state.view.split_borders[0].clone();
@@ -2620,7 +2656,7 @@ mod tests {
         assert!(app
             .state
             .find_border_at(border.pos.saturating_sub(1), row)
-            .is_some());
+            .is_none());
         assert!(app.state.find_border_at(border.pos, row).is_some());
         assert!(app
             .state
@@ -2634,6 +2670,7 @@ mod tests {
         app.state.workspaces = vec![Workspace::test_new("test")];
         app.state.active = Some(0);
         app.state.selected = 0;
+        app.state.pane_gaps = false;
         app.state.workspaces[0].test_split(Direction::Vertical);
         crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 106, 20));
         let border = app.state.view.split_borders[0].clone();
@@ -2642,7 +2679,7 @@ mod tests {
         assert!(app
             .state
             .find_border_at(col, border.pos.saturating_sub(1))
-            .is_some());
+            .is_none());
         assert!(app.state.find_border_at(col, border.pos).is_some());
         assert!(app
             .state
@@ -2651,6 +2688,101 @@ mod tests {
     }
 
     #[test]
+    fn borderless_no_gap_split_has_no_mouse_hitbox_over_content() {
+        let mut app = app_for_mouse_test();
+        app.state.workspaces = vec![Workspace::test_new("test")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.pane_borders = false;
+        app.state.workspaces[0].test_split(Direction::Horizontal);
+        crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 106, 20));
+        let border = app.state.view.split_borders[0].clone();
+        let row = border.area.y.saturating_add(1);
+
+        assert!(app.state.find_border_at(border.pos, row).is_none());
+    }
+
+    #[test]
+    fn bordered_pane_gaps_keep_both_split_borders_draggable() {
+        let mut app = app_for_mouse_test();
+        app.state.workspaces = vec![Workspace::test_new("test")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.pane_gaps = true;
+        app.state.workspaces[0].test_split(Direction::Horizontal);
+        crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 106, 20));
+        let border = app.state.view.split_borders[0].clone();
+        let row = border.area.y.saturating_add(1);
+
+        assert!(app
+            .state
+            .find_border_at(border.pos.saturating_sub(1), row)
+            .is_some());
+        assert!(app.state.find_border_at(border.pos, row).is_some());
+        assert!(app
+            .state
+            .find_border_at(border.pos.saturating_add(1), row)
+            .is_none());
+    }
+
+    #[test]
+    fn borderless_pane_gap_is_not_a_pane_but_remains_split_draggable() {
+        let mut app = app_for_mouse_test();
+        app.state.workspaces = vec![Workspace::test_new("test")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.pane_borders = false;
+        app.state.pane_gaps = true;
+        app.state.workspaces[0].test_split(Direction::Horizontal);
+        crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 106, 20));
+        let border = app.state.view.split_borders[0].clone();
+        let row = border.area.y.saturating_add(1);
+        let gap_col = border.pos.saturating_sub(1);
+
+        assert!(app.state.pane_at(gap_col, row).is_none());
+        assert!(app.state.find_border_at(gap_col, row).is_some());
+        assert!(app.state.find_border_at(border.pos, row).is_none());
+    }
+
+    #[test]
+    fn borderless_gap_hitbox_is_empty_when_first_split_side_has_one_cell() {
+        let mut app = app_for_mouse_test();
+        app.state.workspaces = vec![Workspace::test_new("test")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.pane_borders = false;
+        app.state.pane_gaps = true;
+        app.state.workspaces[0].test_split(Direction::Horizontal);
+        crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 2, 4));
+        let border = app.state.view.split_borders[0].clone();
+        let row = border.area.y.saturating_add(1);
+        let candidate_gap_col = border.pos.saturating_sub(1);
+
+        assert!(app.state.pane_frame_at(candidate_gap_col, row).is_some());
+        assert!(app.state.find_border_at(candidate_gap_col, row).is_none());
+    }
+
+    #[test]
+    fn borderless_gap_hitbox_is_empty_when_first_split_side_has_zero_width() {
+        let mut app = app_for_mouse_test();
+        app.state.workspaces = vec![Workspace::test_new("test")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.pane_borders = false;
+        app.state.pane_gaps = true;
+        app.state.workspaces[0].test_split(Direction::Horizontal);
+        app.state.workspaces[0].tabs[0]
+            .layout
+            .set_ratio_at(&[], 0.1);
+        crate::ui::compute_view(&mut app.state, Rect::new(0, 0, 1, 4));
+        let border = app.state.view.split_borders[0].clone();
+        let row = border.area.y.saturating_add(1);
+
+        assert_eq!(border.pos, 0);
+        assert!(app.state.find_border_at(0, row).is_none());
+    }
+
+    #[test]
     fn selecting_from_right_pane_first_content_column_starts_selection() {
         let mut app = app_for_mouse_test();
         let mut ws = Workspace::test_new("test");
diff --git a/src/app/input/selection.rs b/src/app/input/selection.rs
index 0ccb5506..a66509f0 100644
--- a/src/app/input/selection.rs
+++ b/src/app/input/selection.rs
@@ -189,6 +189,7 @@ mod autoscroll_tests {
             rect: Rect::new(0, 0, 80, 24),
             inner_rect: Rect::new(0, 0, 80, 24),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::NONE,
             is_focused: true,
         });
         (state, pane_id)
@@ -207,6 +208,7 @@ mod autoscroll_tests {
             rect: Rect::new(0, 5, 80, 24),
             inner_rect: Rect::new(0, 5, 80, 24),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::NONE,
             is_focused: true,
         });
         // Anchor at (5, 10), drag to different cell above pane
diff --git a/src/app/mod.rs b/src/app/mod.rs
index 0b944cdf..4fd94697 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -598,6 +598,8 @@ impl App {
             mouse_scroll_lines: config.ui.mouse_scroll_lines(),
             confirm_close: config.ui.confirm_close,
             prompt_new_tab_name: config.ui.prompt_new_tab_name,
+            pane_borders: config.ui.pane_borders,
+            pane_gaps: config.ui.pane_gaps,
             show_agent_labels_on_pane_borders: config.ui.show_agent_labels_on_pane_borders,
             pane_history_persistence: config.experimental.pane_history,
             reveal_hidden_cursor_for_cjk_ime: config.experimental.reveal_hidden_cursor_for_cjk_ime,
@@ -1327,6 +1329,8 @@ impl App {
                     config.ui.right_click_passthrough_modifiers();
                 self.state.confirm_close = config.ui.confirm_close;
                 self.state.prompt_new_tab_name = config.ui.prompt_new_tab_name;
+                self.state.pane_borders = config.ui.pane_borders;
+                self.state.pane_gaps = config.ui.pane_gaps;
                 self.state.show_agent_labels_on_pane_borders =
                     config.ui.show_agent_labels_on_pane_borders;
                 self.state.agent_panel_sort =
diff --git a/src/app/runtime.rs b/src/app/runtime.rs
index e3d5bc92..b8f8091b 100644
--- a/src/app/runtime.rs
+++ b/src/app/runtime.rs
@@ -697,6 +697,7 @@ mod tests {
             rect: ratatui::layout::Rect::new(0, 0, 80, 24),
             inner_rect: ratatui::layout::Rect::new(0, 0, 80, 24),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::NONE,
             is_focused: true,
         });
         (app, pane_id)
@@ -933,6 +934,7 @@ mod tests {
             rect: ratatui::layout::Rect::new(0, 0, cols, rows),
             inner_rect: ratatui::layout::Rect::new(0, 0, cols, rows),
             scrollbar_rect: None,
+            borders: ratatui::widgets::Borders::NONE,
             is_focused: true,
         });
         (app, pane_id)
diff --git a/src/app/state.rs b/src/app/state.rs
index 55d41358..9e5dbed1 100644
--- a/src/app/state.rs
+++ b/src/app/state.rs
@@ -1019,6 +1019,7 @@ pub(crate) enum DragTarget {
         path: Vec<bool>,
         direction: Direction,
         area: Rect,
+        grab_offset: u16,
     },
     PaneScrollbar {
         pane_id: crate::layout::PaneId,
@@ -1361,6 +1362,8 @@ pub struct AppState {
     pub mouse_scroll_lines: usize,
     pub confirm_close: bool,
     pub prompt_new_tab_name: bool,
+    pub pane_borders: bool,
+    pub pane_gaps: bool,
     pub show_agent_labels_on_pane_borders: bool,
     pub pane_history_persistence: bool,
     /// Expose the focused pane's cursor anchor to the outer terminal even when
@@ -1715,6 +1718,8 @@ impl AppState {
             mouse_scroll_lines: crate::config::DEFAULT_MOUSE_SCROLL_LINES,
             confirm_close: true,
             prompt_new_tab_name: true,
+            pane_borders: true,
+            pane_gaps: false,
             show_agent_labels_on_pane_borders: false,
             pane_history_persistence: false,
             reveal_hidden_cursor_for_cjk_ime: false,