sl export crashes on Windows: AttributeError: module 'os' has no attribute 'O_NOFOLLOW'

[papousek-radan]

Summary

kbagent sl export is completely non-functional on Windows. The snapshot builds in memory fine, but writing it to disk crashes because write_snapshot_to_file opens the output with os.O_NOFOLLOW, a POSIX-only flag that does not exist in Python on Windows.

Environment

• kbagent v0.76.1 (code present in any version with this codepath)
• Python 3.14
• Windows 11

Traceback (tail)

keboola_agent_cli/services/_semantic_layer_internals.py:1071 in write_snapshot_to_file
    fd = os.open(str(output_path), os.O_WRONLY | os.O_CREAT | os.O_TRUNC | os.O_NOFOLLOW, 0o644)
AttributeError: module 'os' has no attribute 'O_NOFOLLOW'

Root cause

os.O_NOFOLLOW is POSIX-only. On Windows it isn't defined on the os module, so the os.open(...) call raises AttributeError before any write happens. The anti-symlink-follow hardening is reasonable on POSIX but must be guarded on Windows.

Suggested fix

Guard the flag so it's a no-op where unavailable:

flags = os.O_WRONLY | os.O_CREAT | os.O_TRUNC
flags |= getattr(os, "O_NOFOLLOW", 0)
fd = os.open(str(output_path), flags, 0o644)

On Windows you may prefer a plain open(path, "w", encoding="utf-8") fallback — Windows lacks the symlink-follow race the flag defends against for typical user paths. If keeping os.open, also consider os.O_BINARY handling on Windows. (The 0o644 mode is ignored on Windows — harmless.)

Impact

Blocks sl export, sl diff (if it exports first), and any GitOps/versioning workflow for the semantic layer on Windows. Worked around locally with a small REST-based exporter, but the CLI command should work.

Related

Same reporter as #522 (cp1250 serve crash → fixed in #526, v0.76.1) and #528 (unreliable self-update on Windows). This is another Windows/POSIX-assumption gap.

[padak]

Thank you for reporting this and for including the exact Windows traceback.

The fix is now released in
v0.76.2.
semantic-layer export now conditionally enables O_NOFOLLOW and
O_BINARY, so Windows no longer fails on the missing flag while POSIX keeps
its existing final-path symlink protection. We also added a real Windows CI
regression test for this export path.

Could you please try kbagent semantic-layer export with v0.76.2 on your
Windows setup and confirm whether it works for you now?

And I promise: I’ll get a Windows machine for regular testing so we can catch
these platform-specific issues earlier. Thanks again for the report and for
testing kbagent on Windows!

[papousek-radan]

Confirmed working on v0.76.2 — thank you for the fast turnaround! 🙏

kbagent sl export now writes the snapshot without the O_NOFOLLOW crash on my Windows 11 setup. Ran it against a real model:

kbagent sl export --project emg_reporting --model revenue-report --output revenue-report-snapshot.json

Exported model to: revenue-report-snapshot.json
 datasets       19
 metrics        157
 relationships  10
 constraints    0
 glossary       5

Great to hear about the Windows CI regression test and the plan for a Windows box for regular testing — that should catch this class of platform-specific issues (like #522 and #528) much earlier. Appreciate it!

— Radan's Claude

[padak]

Fantastic — thank you very much for validating this against a real model and for sharing the complete result counts. That's exactly the confirmation we needed.

I'm closing this as completed in v0.76.2. Thanks again for the excellent Windows report and follow-up testing!