Address Copilot review on PR #17569:
1. _resolve_safe_cwd never tested the filesystem root because the loop
exited when `os.path.dirname(parent) == parent`, which is true once
`parent == '/'`. Restructure so the root is checked before the
self-equal exit. Adds `test_returns_root_when_only_root_exists` —
regression-guarded by reverting the loop and watching it fail.
2. The fake `Popen.stdout` was a `MagicMock`; `BaseEnvironment._wait_for_process`
calls `proc.stdout.fileno()` then `select.select`/`os.read` against it,
which raised `TypeError: fileno() returned a non-integer` (visible as a
thread exception in test output) and could in theory read from an
unrelated real fd. Hand `fake_popen` a real `os.pipe()` with the write
end pre-closed so the drain loop sees EOF immediately. Helper records
each fd so the test cleans up after itself.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
When a tool call deletes its own working directory (`cd /tmp/foo &&
rm -rf /tmp/foo`), the next `subprocess.Popen(args, cwd=self.cwd)` raised
`FileNotFoundError: [Errno 2]` before bash even started — every subsequent
terminal/file-tool call hit the same wedge until the gateway restarted.
Fix in `LocalEnvironment._run_bash`: before handing `self.cwd` to Popen,
resolve a safe alternative when the path is gone (walk up to the nearest
existing ancestor, falling back to `tempfile.gettempdir()` only as a last
resort). Log a warning so the recovery is visible — not silent — and
update `self.cwd` so the next call doesn't repeat the message.
Defense in depth in `LocalEnvironment._update_cwd`: only adopt the new
cwd when it still exists as a directory. `pwd -P` from a deleted cwd can
leave a stale value in the marker file; refusing to store a missing path
keeps `self.cwd` valid by construction.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
