DRAFT: fix: disable posix_spawn on Python 3.13+ to fix libtmux race condition

[neubig]

Summary

This PR fixes the Docker/Apptainer sandboxed server example tests failing in CI (issue #1886) without downgrading Python 3.13.

Root Cause Analysis

Python 3.13 made a significant change to subprocess behavior (gh-113117):

"The subprocess module now uses the posix_spawn() function in more situations, including when close_fds is True (the default) on many modern platforms."

This causes a race condition in libtmux where:

1. server.new_session() creates a tmux session via tmux new-session
2. Immediately after, it queries via list-sessions to get full session info
3. With Python 3.13's faster posix_spawn(), the query can execute before tmux has fully registered the session

The Fix

This PR disables posix_spawn specifically for Python 3.13+ before importing libtmux:

if sys.version_info >= (3, 13) and hasattr(subprocess, "_USE_POSIX_SPAWN"):
    subprocess._USE_POSIX_SPAWN = False

This is the official control knob provided by Python 3.13:

"A private control knob subprocess._USE_POSIX_SPAWN can be set to False if you need to force subprocess to never use posix_spawn()."

Alternative to PR #1910

This approach allows us to keep Python 3.13 in the Docker image instead of downgrading to Python 3.12.

Testing

The test-examples label triggers CI to:

1. Build a new Docker image with this fix
2. Run the example tests against that new image

Note: Local testing cannot verify this fix because it requires a Docker image built with the fix. The pre-built latest-python image doesn't contain the fix.

Fixes #1886

[github-actions]

🔄 Running Examples with openhands/claude-haiku-4-5-20251001

Generated: 2026-02-04 22:20:25 UTC

Example	Status	Duration	Cost
01_standalone_sdk/02_custom_tools.py	✅ PASS	23.5s	$0.03
01_standalone_sdk/03_activate_skill.py	✅ PASS	16.2s	$0.03
01_standalone_sdk/05_use_llm_registry.py	✅ PASS	8.6s	$0.01
01_standalone_sdk/07_mcp_integration.py	✅ PASS	35.0s	$0.03
01_standalone_sdk/09_pause_example.py	✅ PASS	13.6s	$0.01
01_standalone_sdk/10_persistence.py	✅ PASS	26.2s	$0.02
01_standalone_sdk/11_async.py	✅ PASS	33.3s	$0.04
01_standalone_sdk/12_custom_secrets.py	✅ PASS	12.9s	$0.01
01_standalone_sdk/13_get_llm_metrics.py	✅ PASS	16.5s	$0.01
01_standalone_sdk/14_context_condenser.py	✅ PASS	3m 54s	$0.52
01_standalone_sdk/17_image_input.py	✅ PASS	14.4s	$0.02
01_standalone_sdk/18_send_message_while_processing.py	✅ PASS	23.0s	$0.01
01_standalone_sdk/19_llm_routing.py	✅ PASS	11.0s	$0.02
01_standalone_sdk/20_stuck_detector.py	✅ PASS	17.3s	$0.02
01_standalone_sdk/21_generate_extraneous_conversation_costs.py	✅ PASS	7.1s	$0.00
01_standalone_sdk/22_anthropic_thinking.py	✅ PASS	11.5s	$0.01
01_standalone_sdk/23_responses_reasoning.py	✅ PASS	1m 15s	$0.01
01_standalone_sdk/24_planning_agent_workflow.py	✅ PASS	3m 14s	$0.24
01_standalone_sdk/25_agent_delegation.py	✅ PASS	1m 38s	$0.15
01_standalone_sdk/26_custom_visualizer.py	✅ PASS	14.3s	$0.02
01_standalone_sdk/28_ask_agent_example.py	❌ FAIL Exit code 1	33.6s	--
01_standalone_sdk/29_llm_streaming.py	✅ PASS	46.5s	$0.03
01_standalone_sdk/30_tom_agent.py	❌ FAIL Exit code 1	2.3s	--
01_standalone_sdk/31_iterative_refinement.py	✅ PASS	3m 30s	$0.25
01_standalone_sdk/32_configurable_security_policy.py	✅ PASS	16.9s	$0.02
01_standalone_sdk/34_critic_example.py	✅ PASS	1m 6s	$0.00
02_remote_agent_server/01_convo_with_local_agent_server.py	✅ PASS	1m 1s	$0.07
02_remote_agent_server/02_convo_with_docker_sandboxed_server.py	❌ FAIL Exit code 1	41.5s	--
02_remote_agent_server/03_browser_use_with_docker_sandboxed_server.py	❌ FAIL Exit code 1	15.0s	--
02_remote_agent_server/04_convo_with_api_sandboxed_server.py	❌ FAIL Exit code 1	1m 9s	--
02_remote_agent_server/05_vscode_with_docker_sandboxed_server.py	❌ FAIL Exit code 1	12.7s	--
02_remote_agent_server/07_convo_with_cloud_workspace.py	✅ PASS	32.2s	$0.03
02_remote_agent_server/08_convo_with_apptainer_sandboxed_server.py	❌ FAIL Exit code 1	2m 42s	--
04_llm_specific_tools/01_gpt5_apply_patch_preset.py	✅ PASS	20.6s	$0.02
04_llm_specific_tools/02_gemini_file_tools.py	✅ PASS	45.8s	$0.07
05_skills_and_plugins/01_loading_agentskills/main.py	✅ PASS	8.5s	$0.01
05_skills_and_plugins/02_loading_plugins/main.py	✅ PASS	4.8s	$0.01

---

❌ Some tests failed

Total: 37 | Passed: 30 | Failed: 7 | Total Cost: $1.76

Failed examples:

• examples/01_standalone_sdk/28_ask_agent_example.py: Exit code 1
• examples/01_standalone_sdk/30_tom_agent.py: Exit code 1
• examples/02_remote_agent_server/02_convo_with_docker_sandboxed_server.py: Exit code 1
• examples/02_remote_agent_server/03_browser_use_with_docker_sandboxed_server.py: Exit code 1
• examples/02_remote_agent_server/04_convo_with_api_sandboxed_server.py: Exit code 1
• examples/02_remote_agent_server/05_vscode_with_docker_sandboxed_server.py: Exit code 1
• examples/02_remote_agent_server/08_convo_with_apptainer_sandboxed_server.py: Exit code 1

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[openhands-ai]

Looks like there are a few issues preventing this PR from being merged!

• GitHub Actions are failing:
  • Run Examples Scripts

If you'd like me to help, just leave a comment, like

@OpenHands please fix the failing actions on PR #1912 at branch `fix/python313-libtmux-race-condition`

Feel free to include any additional details that might help me get this PR into a better state.

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