fix(composer): use wrap_input_lines_for_mouse, clamp selection to input length

- Replace visible_line_char_ranges with wrap_input_lines_for_mouse for accurate mouse selection
- Clamp selection_anchor and cursor_position to char_count
- Clear selection on history navigation to prevent stale highlights
- Add test for history-navigation-clears-stale-selection

crates/tui/src/tui/app.rs

@@ -3774,8 +3774,9 @@ impl App {
     /// Return the (start, end) of the active selection, or `None`.
     /// `start` is inclusive, `end` is exclusive; both are char indices.
     pub fn selection_range(&self) -> Option<(usize, usize)> {
-        let anchor = self.selection_anchor?;
-        let cursor = self.cursor_position;
+        let total = char_count(&self.input);
+        let anchor = self.selection_anchor?.min(total);
+        let cursor = self.cursor_position.min(total);
         if anchor == cursor {
             return None;
         }
@@ -4510,6 +4511,7 @@ impl App {
         self.history_index = Some(new_index);
         self.input = self.input_history[new_index].clone();
         self.cursor_position = char_count(&self.input);
+        self.selection_anchor = None;
         self.selected_attachment_index = None;
         self.slash_menu_hidden = false;
         self.paste_burst.clear_after_explicit_paste();
@@ -4526,6 +4528,7 @@ impl App {
                     self.history_index = Some(i + 1);
                     self.input = self.input_history[i + 1].clone();
                     self.cursor_position = char_count(&self.input);
+                    self.selection_anchor = None;
                     self.selected_attachment_index = None;
                     self.slash_menu_hidden = false;
                     self.paste_burst.clear_after_explicit_paste();
@@ -4534,6 +4537,7 @@ impl App {
                     if let Some(draft) = self.history_navigation_draft.take() {
                         self.input = draft.input;
                         self.cursor_position = draft.cursor.min(char_count(&self.input));
+                        self.selection_anchor = None;
                         self.selected_attachment_index = None;
                         self.slash_menu_hidden = false;
                         self.paste_burst.clear_after_explicit_paste();
@@ -5914,6 +5918,22 @@ mod tests {
         assert!(app.history_index.is_none());
     }
 
+    #[test]
+    fn input_history_navigation_clears_stale_selection() {
+        let mut app = App::new(test_options(false), &Config::default());
+        app.input_history.push("previous input".to_string());
+        app.input = "hello world".to_string();
+        app.cursor_position = "hello ".chars().count();
+        app.selection_anchor = Some(app.input.chars().count());
+
+        app.history_up();
+        assert_eq!(app.input, "previous input");
+        assert!(app.selection_anchor.is_none());
+
+        app.insert_char('x');
+        assert_eq!(app.input, "previous inputx");
+    }
+
     #[test]
     fn input_history_restores_empty_draft_at_end_of_navigation() {
         let mut app = App::new(test_options(false), &Config::default());

crates/tui/src/tui/widgets/mod.rs

@@ -667,12 +667,13 @@ impl Renderable for ComposerWidget<'_> {
                 Style::default().fg(palette::TEXT_MUTED).italic(),
             )));
         } else if let Some((sel_start, sel_end)) = self.app.selection_range() {
-            let line_ranges = visible_line_char_ranges(
-                &self.app.input,
-                &visible_lines,
-                content_width,
-                scroll_offset,
-            );
+            let line_ranges: Vec<(usize, usize)> =
+                wrap_input_lines_for_mouse(&self.app.input, content_width)
+                    .into_iter()
+                    .skip(scroll_offset)
+                    .take(visible_lines.len())
+                    .map(|(start, text)| (start, start + text.chars().count()))
+                    .collect();
             for (line_text, (line_start, line_end)) in visible_lines.iter().zip(line_ranges.iter())
             {
                 let spans = line_spans_with_selection(
@@ -2443,58 +2444,6 @@ fn wrap_text(text: &str, width: usize) -> Vec<String> {
     lines
 }
 
-/// Compute the (char_start, char_end) range for each visible wrapped line.
-/// `char_start` is inclusive, `char_end` is exclusive.
-/// `scroll_offset` is the number of wrapped lines skipped from the top.
-fn visible_line_char_ranges(
-    input: &str,
-    visible_lines: &[String],
-    width: usize,
-    scroll_offset: usize,
-) -> Vec<(usize, usize)> {
-    if input.is_empty() || width == 0 {
-        return vec![(0, 0); visible_lines.len()];
-    }
-
-    let mut ranges = Vec::new();
-    let mut char_idx = 0usize;
-    let mut line_start = 0usize;
-    let mut line_width = 0usize;
-
-    for g in input.graphemes(true) {
-        if g == "\n" {
-            ranges.push((line_start, char_idx));
-            char_idx += 1;
-            line_start = char_idx;
-            line_width = 0;
-            continue;
-        }
-
-        let gw = g.width();
-        if line_width + gw > width && line_width > 0 {
-            ranges.push((line_start, char_idx));
-            line_start = char_idx;
-            line_width = 0;
-        }
-        char_idx += g.chars().count();
-        line_width += gw;
-        if line_width >= width {
-            ranges.push((line_start, char_idx));
-            line_start = char_idx;
-            line_width = 0;
-        }
-    }
-    ranges.push((line_start, char_idx));
-
-    // Use the actual scroll_offset to align with visible_lines.
-    let start = scroll_offset.min(ranges.len());
-    ranges
-        .into_iter()
-        .skip(start)
-        .take(visible_lines.len())
-        .collect()
-}
-
 fn line_spans_with_selection<'a>(
     line: &'a str,
     line_start: usize,