fix: use cell-edge diagonals for diff gap hatching

docs/editing.md

@@ -217,7 +217,7 @@ File rows show colored **A** (added, green), **M** (modified, yellow), **D** (re
 
 Changed text rows use muted red backgrounds in Before and muted green backgrounds in After, including blank tails and real empty lines. Foreground colors use the editor's bundled Tree-sitter syntax highlighting, parsed independently for each snapshot and its path (including the old path for renames). Unknown languages retain the normal foreground; historical snapshots do not borrow live-buffer LSP tokens.
 
-Missing counterparts use adjacent muted `/` stripes on the normal terminal background instead of blank rows, with a slash in every column. The dense pattern stays continuous while scrolling. Actual empty source lines retain their normal/change background and are not hatched.
+Missing counterparts use adjacent muted `╱` diagonals (U+2571, box drawings light diagonal) on the normal terminal background, one per column. Unlike the text slash `/`, this glyph is designed to reach cell corners so diagonals can join end to end across successive rows. Pixel-perfect joins depend on the terminal's font and line-spacing rendering. Actual empty source lines retain their normal/change background and are not hatched.
 
 Tab/Shift+Tab cycles focus between Files, Before, and After. In text panes, Up/Down or Ctrl+j/k scrolls both panes together; Left/Right or Ctrl+h/l scrolls the focused pane horizontally. Home/End goes to the first/last tree row or aligned text row. Wheel input over a text pane scrolls both panes; over Files it navigates visible tree rows without opening them. Esc first leaves filtering when the tree is focused; otherwise it closes the diff and preserves the editor's buffers, cursors, unsaved text, and undo history. Typing and pasted text cannot edit either snapshot.
 

src/tui.rs

@@ -1297,7 +1297,7 @@ fn draw_diff_pane(
             let buffer = frame.buffer_mut();
             for x in 0..content.width {
                 buffer[(content.x + x, row_area.y)]
-                    .set_symbol("/")
+                    .set_symbol("╱")
                     .set_style(style);
             }
             continue;
@@ -2567,7 +2567,7 @@ mod tests {
         let gap_symbols: Vec<_> = (after.x + 1..after.right() - 1)
             .map(|x| {
                 let cell = &buffer[(x, y)];
-                assert_eq!(cell.symbol(), "/");
+                assert_eq!(cell.symbol(), "╱");
                 assert_eq!(cell.bg, Color::Reset);
                 assert_eq!(cell.fg, Color::Rgb(72, 72, 72));
                 cell.symbol().to_owned()
@@ -2617,7 +2617,7 @@ mod tests {
             let y = before.y + 1 + offset;
             for x in before.x + 1..before.right() - 1 {
                 let cell = &buffer[(x, y)];
-                assert_eq!(cell.symbol(), "/");
+                assert_eq!(cell.symbol(), "╱");
                 assert_eq!(cell.bg, Color::Reset);
                 assert_eq!(cell.fg, Color::Rgb(72, 72, 72));
             }
@@ -2637,7 +2637,7 @@ mod tests {
         render_diff(&mut terminal, &diff, &mut panels);
         let buffer = terminal.backend().buffer();
         for x in before.x + 1..before.right() - 1 {
-            assert_eq!(buffer[(x, before.y + 1)].symbol(), "/");
+            assert_eq!(buffer[(x, before.y + 1)].symbol(), "╱");
         }
         assert_eq!(buffer[(before.x, before.y + 1)].symbol(), "│");
         assert_eq!(buffer[(before.right() - 1, before.y + 1)].symbol(), "│");