[Bug Report] ./isaaclab.sh --install fails with Isaac Sim 6.0 binaries + conda: "failed to parse CPython sys.version"

Describe the bug

With a pre-built Isaac Sim 6.0 binary linked as _isaac_sim and a conda environment created by ./isaaclab.sh --conda, ./isaaclab.sh --install fails on its very first step (pip install --upgrade pip):

  File "/home/<user>/IsaacLab/_isaac_sim/kit/python/lib/python3.12/platform.py", line 1160, in python_version
  File "/home/<user>/IsaacLab/_isaac_sim/kit/python/lib/python3.12/platform.py", line 1110, in _sys_version
ValueError: failed to parse CPython sys.version: '3.12.14 | packaged by conda-forge | (main, Aug 21 2026, 22:48:28) [GCC 14.4.0]'
[ERROR] Command failed with code 2: ".../envs/env_isaaclab/bin/python -m pip install --upgrade pip"

Note the traceback: the conda interpreter is importing platform.py from Isaac Sim's bundled stdlib, not its own.

Root cause

Isaac Sim 6.0 ships no setup_conda_env.sh, so isaaclab.sh falls back to sourcing _isaac_sim/setup_python_env.sh. That script appends kit/python/lib/python3.12 (the entire stdlib of the bundled interpreter) to PYTHONPATH. PYTHONPATH entries precede the interpreter's own stdlib on sys.path, so every stdlib module that differs between the two builds is shadowed.

The bundled platform.py has an older sys_version_parser regex without the (?:\|[^|]*\|)? group that CPython added for the conda-forge "| packaged by conda-forge |" version string, so platform.python_version() raises. pip calls it when building its user agent, so every pip invocation in the env fails.

isaaclab.sh already prepends the env's site-packages to work around the pip_prebundle shadowing, but that does not help here because the stdlib directory is being shadowed, not a package.

Steps to reproduce

1. Isaac Sim 6.0.0 binary (tested: 6.0.0-rc.59+release.41464.5f2772bc.glapps) at /opt/isaacsim.
2. git clone -b release/3.0.0 https://github.com/isaac-sim/IsaacLab.git && cd IsaacLab && ln -s /opt/isaacsim _isaac_sim
3. ./isaaclab.sh --conda env_isaaclab && conda activate env_isaaclab (creates Python 3.12.14 from conda-forge)
4. ./isaaclab.sh --install → fails as above.

Same code path exists on develop.

System Info

• Commit: release/3.0.0 @ 2799120 (develop has identical isaaclab.sh)
• Isaac Sim: 6.0.0-rc.59 (binary)
• OS: Ubuntu, kernel 7.0
• GPU: RTX 4070 Laptop, driver 595.84
• Python (conda-forge): 3.12.14
• pip: 26.2.1

Proposed fix

After sourcing setup_python_env.sh, strip the kit/python/lib/python3.X stdlib directory from PYTHONPATH (keep Kit's site-packages and extension paths). With that 1-line filter, --install completes and both scripts/tutorials/00_sim/create_empty.py and a rsl_rl Cartpole training run work. PR to follow.

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo