[dalyathan]

Relevant issue or PR

Fixes #883

Description of changes

Loading tesseract_api.py wrote the runtime's whole sys.path into PYTHONPATH, so every subprocess started from it inherited the runtime's stdlib and site-packages. A child running the same interpreter doesn't notice, but a different Python imports the runtime's modules instead of its own. With a 3.14 runtime, a Python 3.11 started from apply dies on start-up:

AssertionError: SRE module mismatch

load_module_from_path now exports only the module directory, ahead of any existing PYTHONPATH, and restores the previous value if loading fails. Children can still import tesseract_api.py and its sibling modules, and the sys.modules registration from #488 is unchanged.

Testing done

• New test test_subprocesses_inherit_only_module_dir_on_pythonpath checks the PYTHONPATH a child process sees, with and without an outer PYTHONPATH. On main the child gets the runtime's full sys.path. test_load_module_from_path_restores_pythonpath_on_failure covers the failure path. Both fail on main and pass with this change.
• The Python 3.11 repro above fails on main and runs with this change.
• The Document sharp edges when using ProcessPoolExecutor in tesseract_api.py #356 case (a spawn ProcessPoolExecutor in apply mapping a function from tesseract_api.py and one from a sibling module) gives the same result before and after.
• pytest --skip-endtoend passes locally (Python 3.14, without the jax extras). Not run: the end-to-end Docker tests and Python 3.10.

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[dalyathan]

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[dalyathan]

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