fix: make Windows unit tests pass

[Eishaan-Khatri]

fixed errors that occurred due to Windows-specific path and file-locking behavior:

• Updated the backlog prioritization test so it checks path parts instead of assuming Unix-style / separators.
• Replaced the POSIX-only fcntl session-file lock with a cross-platform lock helper that uses msvcrt on Windows and keeps fcntl on Unix.
• Verified with uv run pytest tests/unit: 329 passed, 14 warnings

[Eishaan-Khatri]

The Windows unit suite passes locally with uv run pytest tests/unit (329 passed, 14 warnings). The failing Claude PR Review check appears to be a workflow permission issue on fork PRs rather than a code failure.

[Eishaan-Khatri]

I have re-signed the latest commit, so the verified-signature requirement should now be resolved. The remaining failing check appears to be the Claude PR Review workflow permission issue for fork PRs.

I have used Codex for assistance in resolving the issue and creating pr.

[github-actions]

Claude finished @lewtun's task in 2m 0s —— View job

---

Claude PR Review

No blocking issues — 1 P1, 2 P2.

The two fixes are small and targeted, and the test change is the right approach (Path.parts is the canonical way to compare path segments cross-platform). The lock helper works, but the Windows path has a couple of semantic differences from fcntl worth knowing about.

---

P1 — Windows path silently degrades shared lock to exclusive

agent/core/session_uploader.py:304-327

The exclusive keyword is honored on Unix (LOCK_SH vs LOCK_EX) but ignored on Windows: msvcrt.locking only supports exclusive locks (LK_LOCK / LK_NBLCK). There is no LK_SH equivalent. That means _read_session_file (exclusive=False) takes an exclusive lock on Windows, so two concurrent readers serialize where they would not on Unix.

Concrete consequence: the org uploader and the personal uploader subprocesses both call _read_session_file at the start of upload_session_as_file (line 485). On Windows they'll now block each other on that read. Each lock window is short (a single json.load), so the practical risk of LK_LOCK's ~10-second retry budget being exhausted and raising OSError is low — but it is nonzero, and it would surface as a hard failure in the outer except Exception at line 571 with no retry. On Unix the same scenario would just wait.

Two reasonable resolutions, either is fine:

1. Document the divergence in the helper's docstring and accept it (the lock windows really are short).
2. Catch OSError from msvcrt.locking in the Windows branch and degrade to a short bounded retry loop, so contention manifests the same way it does on Unix.

Fix this →

---

P2 — Dead local on Windows branch

agent/core/session_uploader.py:311 — mode = msvcrt.LK_LOCK is just a rename; inlining or dropping it would make the branch a couple of lines shorter. Pre-existing pattern was no intermediate, so this is cosmetic.

P2 — Lock-helper has no Windows-specific test

Existing tests/unit/test_session_uploader.py::test_update_upload_status_preserves_other_uploader_fields does exercise the new helper on every platform, which is enough to catch the obvious regression. A dedicated Windows-only contention test isn't worth the complexity, but it's worth noting the helper's Windows semantics are only covered by the happy path. Informational.

---

Confirmed correct

• tests/unit/test_prioritize_backlog.py:721 — out.parts[-3:-1] == ("scratch", "backlog-prioritization") is the right pattern. Holds across ("/", "scratch", "backlog-prioritization", "20260504T123000Z") on POSIX and ("C:\\", "scratch", "backlog-prioritization", "20260504T123000Z") on Windows.
• The _file_lock finally block correctly re-seeks before LK_UNLCK so a raised exception inside the with doesn't leave the file pointer past the locked byte.
• Locking a single byte at offset 0 is a standard convention for advisory whole-file coordination; both reader and writer use the same byte, so they coordinate correctly.

---

• Read changed files
• Inspect callers of lock helpers (_read_session_file, _update_upload_status are the only call sites; both within upload_session_as_file and retry_failed_uploads)
• Check for prior Claude review (none — first review on this PR)
• Verify cross-platform lock semantics
• Post review
  · fix-windows-unit-suite

[lewtun]

Hi @Eishaan-Khatri thank you for the PR! Please address the Claude review and we can merge :)