fix(generator): 修复diff截断时的字符边界问题

src/generator/mod.rs

@@ -31,7 +31,8 @@ impl ContentGenerator {
         // Truncate diff if too long
         let max_diff_len = 4000;
         let truncated_diff = if diff.len() > max_diff_len {
-            format!("{}\n... (truncated)", &diff[..max_diff_len])
+            let boundary = diff.floor_char_boundary(max_diff_len);
+            format!("{}\n... (truncated)", &diff[..boundary])
         } else {
             diff.to_string()
         };