fix: reject DEL character (0x7F) in input validation (#122)

The reject_control_chars helper rejected bytes 0x00-0x1F but allowed
the DEL character (0x7F), which is also an ASCII control character.
This could allow malformed input from LLM agents to bypass validation.

.changeset/fix-reject-del-char.md

@@ -0,0 +1,9 @@
+---
+"@googleworkspace/cli": patch
+---
+
+fix: reject DEL character (0x7F) in input validation
+
+The `reject_control_chars` helper rejected bytes 0x00–0x1F but allowed
+the DEL character (0x7F), which is also an ASCII control character. This
+could allow malformed input from LLM agents to bypass validation.

src/validate.rs

@@ -118,9 +118,10 @@ pub fn validate_safe_dir_path(dir: &str) -> Result<PathBuf, GwsError> {
     Ok(canonical)
 }
 
-/// Rejects strings containing null bytes or ASCII control characters.
+/// Rejects strings containing null bytes or ASCII control characters
+/// (including DEL, 0x7F).
 fn reject_control_chars(value: &str, flag_name: &str) -> Result<(), GwsError> {
-    if value.bytes().any(|b| b < 0x20) {
+    if value.bytes().any(|b| b < 0x20 || b == 0x7F) {
         return Err(GwsError::Validation(format!(
             "{flag_name} contains invalid control characters"
         )));
@@ -388,6 +389,11 @@ mod tests {
         assert!(reject_control_chars("hello\nworld", "test").is_err());
     }
 
+    #[test]
+    fn test_reject_control_chars_del() {
+        assert!(reject_control_chars("hello\x7Fworld", "test").is_err());
+    }
+
     // -- encode_path_segment --------------------------------------------------
 
     #[test]