isaaclab.sh -p fails with "No module named isaaclab" on binary install (Isaac Sim 5.1.0)

[Ohaginia]

Environment

• Isaac Sim: 5.1.0-rc.19 (binary install, symlinked at IsaacLab/_isaac_sim)
• Isaac Lab: Latest main branch (source at IsaacLab/source/isaaclab/)
• OS: Ubuntu 22.04, Linux 6.8.0
• Python: Kit-bundled Python 3.11 (_isaac_sim/kit/python/bin/python3.11)
• PyTorch: 2.7.0+cu128

Problem

Running any script with isaaclab.sh -p that imports isaaclab fails:

$ isaaclab.sh -p my_script.py --headless
[INFO] Using python from: /home/user/IsaacLab/_isaac_sim/python.sh
ModuleNotFoundError: No module named 'isaaclab'

However, isaacsim imports fine:

>>> import isaacsim  # OK - found at _isaac_sim/python_packages/isaacsim/
>>> import isaaclab   # FAILS

pip list in the kit Python shows 266 packages (torch, ROS2 msgs, etc.) but no isaaclab* packages at all.

The source/isaaclab/setup.py exists on disk but has never been installed into the kit Python environment.

What I tried

1. unset VIRTUAL_ENV && isaaclab.sh -p my_script.py → same error
2. Direct _isaac_sim/python.sh my_script.py → same error
3. Confirmed CONDA_PREFIX is not set

Question

Is isaaclab.sh --install (i.e., isaaclab.sh -i) a required setup step before isaaclab.sh -p can work with a binary Isaac Sim install? The installation docs mention running the installer, but I want to confirm:

1. Is isaaclab.sh -i the correct fix for this?
2. Are there any known issues with isaaclab.sh -i on Isaac Sim 5.1.0-rc.19?
3. Does -i modify the kit Python's site-packages in-place, or does it require a venv/conda env?

Any guidance appreciated. Thanks!