fix: close file descriptor in LocalEnvironment._update_cwd

_update_cwd() uses a bare open(self._cwd_file).read() that never
closes the file descriptor. This method runs on every terminal
command execution, so the fd leaks accumulate in long sessions.

Use a with statement so the fd is released promptly.

Fixes #15552 (standalone resubmission)

tools/environments/local.py

@@ -392,7 +392,8 @@ class LocalEnvironment(BaseEnvironment):
     def _update_cwd(self, result: dict):
         """Read CWD from temp file (local-only, no round-trip needed)."""
         try:
-            cwd_path = open(self._cwd_file).read().strip()
+            with open(self._cwd_file) as f:
+                cwd_path = f.read().strip()
             if cwd_path:
                 self.cwd = cwd_path
         except (OSError, FileNotFoundError):