fix: hide preserved path masks from git status

Represent missing .agents and .codex preserved path masks as read-only empty directories instead of empty files so Git ignores them while cleanup still removes the host mount targets after bwrap exits.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/protocol/src/permissions.rs

@@ -37,6 +37,10 @@ pub fn is_preserved_path_name(name: &OsStr) -> bool {
         .any(|preserved| name == OsStr::new(preserved))
 }
 
+pub fn is_preserved_directory_path_name(name: &OsStr) -> bool {
+    name == OsStr::new(PRESERVED_AGENTS_PATH_NAME) || name == OsStr::new(PRESERVED_CODEX_PATH_NAME)
+}
+
 /// Returns the preserved workspace metadata name when an agent write to `path`
 /// should be blocked before execution.
 pub fn forbidden_agent_preserved_path_write(