fix(terminal): use grapheme_width for accurate column slicing

text_in_cols and text_slice_cols now walk grapheme clusters with
grapheme_width() instead of assuming 1 char = 1 column.  This fixes
column slicing for:
- Wide characters (CJK, emoji) that occupy 2 grid columns
- Combining marks that occupy 0 columns

The prior 1:1 char∶col mapping caused selection-copy and serialize
output to misalign column ranges when wide/combining characters were
present in a row.

- Update roadmap: mark both P0 follow-up items as resolved

TERMINAL_ROADMAP.md

@@ -62,7 +62,7 @@
    - 实现于 `component.rs`（`Selection`/`selection_rects`/`point_to_cell`/鼠标处理）+ `core.rs::selection_text` + `core.rs::TerminalRow::text_in_cols`，均有单元测试。
 3. **快捷键**：Ctrl-Shift-C 复制 / Ctrl-V 粘贴。
 
-**已知后续项（非阻塞）**：拖拽到视窗边缘时**没有自动滚动延伸选区**（需先滚到位再选）；行内 wide+组合字符混排的列切片为近似。
+**已知后续项（非阻塞）**：拖拽到视窗边缘时**没有自动滚动延伸选区**（✅ 已通过上一轮 auto-scroll 实现）；行内 wide+组合字符混排的列切片（✅ 已通过 grapheme_width 修正 text_in_cols / text_slice_cols）。
 
 ---
 

app/src/terminal/core.rs

@@ -821,15 +821,22 @@ impl TerminalRow {
             if col >= to {
                 break;
             }
-            // This segment overlaps [from, to): emit the columns inside range.
-            let chars: Vec<char> = seg.text.chars().collect();
-            for (i, ch) in chars.iter().enumerate() {
-                // Distribute chars across the segment's columns 1:1 (clamped).
-                let ch_col = col + i.min(seg.cols.saturating_sub(1));
-                if ch_col >= from && ch_col < to {
-                    out.push(*ch);
+            // Walk grapheme clusters and track actual grid-column width so
+            // that wide chars (2 cols) and combining marks (0 cols) are
+            // sliced correctly.
+            use unicode_segmentation::UnicodeSegmentation;
+            for grapheme in UnicodeSegmentation::graphemes(seg.text.as_str(), true) {
+                let w = grapheme_width(grapheme, false);
+                let ch_end = col + w;
+                // If this grapheme overlaps [from, to), emit it.
+                if ch_end > from && col < to {
+                    out.push_str(grapheme);
                 }
+                col = ch_end;
             }
+            // If our tracked `col` differs from `seg_end` (e.g. because
+            // `grapheme_width` disagrees with the vt100 grid), trust the
+            // grid column count for the next segment's baseline.
             col = seg_end;
         }
         out.trim_end().to_owned()
@@ -947,9 +954,21 @@ fn rfind_literal_before_col(text: &str, query: &str, before_col: usize) -> Optio
 }
 
 fn text_slice_cols(text: &str, start_col: usize, end_col: usize) -> String {
-    let start = byte_index_for_char_col(text, start_col);
-    let end = byte_index_for_char_col(text, end_col);
-    text.get(start..end).unwrap_or_default().to_owned()
+    use unicode_segmentation::UnicodeSegmentation;
+    let mut out = String::new();
+    let mut col = 0usize;
+    for grapheme in UnicodeSegmentation::graphemes(text, true) {
+        let w = grapheme_width(grapheme, false);
+        let ch_end = col + w;
+        if ch_end > start_col && col < end_col {
+            out.push_str(grapheme);
+        }
+        col = ch_end;
+        if col >= end_col {
+            break;
+        }
+    }
+    out
 }
 
 fn byte_index_for_char_col(text: &str, col: usize) -> usize {