fix: retain semantic colors across editable diff updates

src/tui.rs

@@ -13669,6 +13669,34 @@ end
                 }
                 editor.handle(Input::Char('\t'));
             }
+            if writable {
+                while editor.diff_buffer_focus() != Some(Focus::After)
+                    || editor.diff().unwrap().focus != Focus::After
+                {
+                    editor.handle(Input::Char('\t'));
+                }
+                assert!(editor.diff_editing());
+                editor.handle(Input::Char('A'));
+                assert_eq!(editor.mode(), Mode::Insert);
+                for input in " // typing".chars().map(Input::Char).chain([
+                    Input::Escape,
+                    Input::Char('u'),
+                    Input::Char('U'),
+                ]) {
+                    editor.handle(input.clone());
+                    terminal
+                        .draw(|frame| views.draw(frame, &mut editor))
+                        .unwrap();
+                    let regions = views.panels.diff.as_ref().unwrap().regions;
+                    for (index, color) in [(1, Color::LightCyan), (2, Color::LightBlue)] {
+                        let pane = regions[index].0;
+                        let cell = &terminal.backend().buffer()[(pane.x + 8, pane.y + 1)];
+                        assert_eq!(cell.symbol(), "v");
+                        assert_eq!(cell.fg, color, "semantic color flashed after {input:?}");
+                    }
+                }
+                assert_eq!(editor.lines(), ["let value = 2; // typing"]);
+            }
             editor
                 .replace_semantic_tokens(editor.buffer_id(), editor.text_revision(), None)
                 .unwrap();
@@ -15084,8 +15112,9 @@ end
             assert_eq!(buffer[(0, 0)].fg, Color::Reset);
             assert_eq!(editor.lines(), &[source]);
         }
-        editor.handle(Input::Char('x'));
-        assert!(editor.semantic_tokens().is_empty());
+        editor
+            .replace_semantic_tokens(editor.buffer_id(), editor.text_revision(), None)
+            .unwrap();
         let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(20, 4)).unwrap();
         let (mut top, mut left) = (0, 0);
         terminal