Gate follow-ups on the converged head, all fail-closed hardening with no
contradiction to the existing security model:
- _as_posix_path rejects embedded null bytes (returns None).
- _safe_resolve catches ValueError (null-byte .resolve()) -> raw path so the
block gate rejects cleanly.
- _workspace_access_error returns a clean 'Invalid path' validation error on
stat() ValueError instead of an uncaught 500.
- /api/workspaces/add route preflight resolve() now catches
(ValueError, OSError, RuntimeError) -> clean 400.
Reconciliation note: an interim gate suggestion to restore ~user/~root
expansion and block /root was REVERTED — the full suite surfaced
tests/test_batch_fixes.py::TestRootWorkspaceUnblocked, which pins the
deliberate #510/#521 decision that /root is NOT blocked (Hermes runs as root
in many deployments, where /root is the legitimate home, allowed via the home
carve-out). Expanding ~root for a non-root deployment would register root's
home, so the PR's original 'leave ~user literal' behavior is the correct,
safer choice. Kept only the null-byte fixes; added a guard test pinning that
/root stays unblocked.
Co-authored-by: rodboev <rodboev@users.noreply.github.com>
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