fix: use safe_truncate to truncate charactor (#3263) (#3264)

Signed-off-by: toyamagu2021@gmail.com <toyamagu2021@gmail.com>

crates/goose/src/utils.rs

@@ -0,0 +1,49 @@
+/// Safely truncate a string at character boundaries, not byte boundaries
+///
+/// This function ensures that multi-byte UTF-8 characters (like Japanese, emoji, etc.)
+/// are not split in the middle, which would cause a panic.
+///
+/// # Arguments
+/// * `s` - The string to truncate
+/// * `max_chars` - Maximum number of characters to keep
+///
+/// # Returns
+/// A truncated string with "..." appended if truncation occurred
+pub fn safe_truncate(s: &str, max_chars: usize) -> String {
+    if s.chars().count() <= max_chars {
+        s.to_string()
+    } else {
+        let truncated: String = s.chars().take(max_chars.saturating_sub(3)).collect();
+        format!("{}...", truncated)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_safe_truncate_ascii() {
+        assert_eq!(safe_truncate("hello world", 20), "hello world");
+        assert_eq!(safe_truncate("hello world", 8), "hello...");
+        assert_eq!(safe_truncate("hello", 5), "hello");
+        assert_eq!(safe_truncate("hello", 3), "...");
+    }
+
+    #[test]
+    fn test_safe_truncate_japanese() {
+        // Japanese characters: "こんにちは世界" (Hello World)
+        let japanese = "こんにちは世界";
+        assert_eq!(safe_truncate(japanese, 10), japanese);
+        assert_eq!(safe_truncate(japanese, 5), "こん...");
+        assert_eq!(safe_truncate(japanese, 7), japanese);
+    }
+
+    #[test]
+    fn test_safe_truncate_mixed() {
+        // Mixed ASCII and Japanese
+        let mixed = "Hello こんにちは";
+        assert_eq!(safe_truncate(mixed, 20), mixed);
+        assert_eq!(safe_truncate(mixed, 8), "Hello...");
+    }
+}