fix(chat): ensure sanitize_user_prompt handles UTF-8 boundaries correctly (#3087)

Author: h16rkim

crates/chat-cli/src/cli/chat/cli/hooks.rs

@@ -378,8 +378,7 @@ impl HookExecutor {
 
 /// Sanitizes a string value to be used as an environment variable
 fn sanitize_user_prompt(input: &str) -> String {
-    // Limit the size of input to first 4096 characters
-    let truncated = if input.len() > 4096 { &input[0..4096] } else { input };
+    let truncated = truncate_safe(input, 4096);
 
     // Remove any potentially problematic characters
     truncated.replace(|c: char| c.is_control() && c != '\n' && c != '\r' && c != '\t', "")
@@ -742,4 +741,31 @@ mod tests {
         assert_eq!(*exit_code, 0);
         assert!(hook_output.contains("Turn completed successfully"));
     }
+
+    #[test]
+    fn test_sanitize_user_prompt_cjk_characters() {
+        // Test with CJK characters that would cause panic with naive byte slicing
+        let korean_text = "한".repeat(2000); // Each Korean character is 3 bytes in UTF-8
+        let result = sanitize_user_prompt(&korean_text);
+
+        // Should not panic and should be truncated safely
+        assert!(result.len() <= 4096);
+        assert!(!result.is_empty());
+
+        // Test with mixed ASCII and CJK at boundary
+        let mixed_text = "a".repeat(4094) + "한국어"; // 4094 + 9 bytes = 4103 bytes
+        let result = sanitize_user_prompt(&mixed_text);
+        assert!(result.len() <= 4096);
+        assert!(result.ends_with("a")); // Should end with ASCII, not partial CJK
+
+        // Test with text shorter than limit
+        let short_text = "안녕하세요";
+        let result = sanitize_user_prompt(short_text);
+        assert_eq!(result, short_text);
+
+        // Test with control characters
+        let text_with_controls = "Hello\x00World\nTest\r\tEnd";
+        let result = sanitize_user_prompt(text_with_controls);
+        assert_eq!(result, "HelloWorld\nTest\r\tEnd");
+    }
 }