Fix race condition in new_session() by avoiding list-sessions query

[neubig]

Fixes: #624

Previously, new_session() would:

1. Run 'tmux new-session -P -F#{session_id}' to create session
2. Immediately run 'tmux list-sessions' to fetch full session data

This created a race condition in some environments where list-sessions might not see the newly created session yet, causing TmuxObjectDoesNotExist errors.

The fix:

• Expand the -F format string to include all Obj fields (except 'server')
• Parse the output directly into a Session object
• Eliminate the separate list-sessions query entirely

This is more efficient (one fewer subprocess call) and eliminates the race condition by making session creation atomic.

I tested this using the script in the original issue and it works in all three cases:

Environment	Result
Python 3.12 + PyInstaller + Docker	PASS ✓
Python 3.13 + PyInstaller + Docker	PASS ✓
Python 3.13 + PyInstaller + Native	PASS ✓

[CLAassistant]

All committers have signed the CLA.

[tony]

@neubig Thank you. Can you sign the CLA?

Is there a CI or full traceback for this? Any tmux version you're trying with? Thanks for the details in #624.

[neubig]

Thanks @tony! Signed the CLA.

I checked and the version is tmux 3.5a.

And in terms of CI where this failed, the reason why we were able to identify this is because this CI run failed: https://github.com/OpenHands/software-agent-sdk/actions/runs/21638051841/job/62369267088

We were able to trace it back to the upgrade from Python 3.12 to 3.13, and after reverting to 3.12, the consistent failures due to the issue I cited here disappeared (although this particular run still has a few failures): https://github.com/OpenHands/software-agent-sdk/actions/runs/21710957108

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.43%. Comparing base (9da19ba) to head (bc33be0).

Files with missing lines	Patch %	Lines
src/libtmux/neo.py	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #625      +/-   ##
==========================================
+ Coverage   45.39%   45.43%   +0.03%     
==========================================
  Files          22       22              
  Lines        2249     2256       +7     
  Branches      360      360              
==========================================
+ Hits         1021     1025       +4     
- Misses       1082     1085       +3     
  Partials      146      146              

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[tony]

@neubig Thank you very much! I'll look at merging this as a pre-release tomorrow so we can test if it works on your side.

[neubig]

Great, thank you!

[tony]

@neubig (when github is back online): what's the best way for you to test this? Can you pin the branch? Do you need a PyPI release (and would an alpha do?)

Any disagreement / opinion on the changes I made in the PR?

[neubig]

Thanks @tony! I can pin the branch and I'm testing at the moment, will try to get this done this week.

[tony]

@neubig If you have a chance let me know and if you prefer I go for a prerelease on PyPI (if that's easier let me know as well)

[neubig]

Hi @tony, thanks a lot! I was able to test this, and there were two issues (another being the locale settings that were used by pyinstaller). But this solved part of the problem, so I think it's good!