Fix: Stop swallowing ImportError when loading micro simulation

[Geethapranay1]

Fix #258

Previously, load_backend_class swallowed ImportError inside the try_load block. This hid the real error (like a missing dependency such as foamlib) and just threw a generic "Could not load micro simulation" error.
I moved the import_module call out of the try...except block so that ModuleNotFoundError bubbles up properly. I also added some tests to verify that missing direct and transitive dependencies report the correct error, while making sure the old fallback logic still works if the file loads but the class is missing

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[Geethapranay1]

@IshaanDesai PTAL!

[IshaanDesai]

@fsimonis can you please test this with the foamlib case?

[fsimonis]

This works, but doesn't give additional context.

[IshaanDesai]

This works, but doesn't give additional context.

Okay. So the ImportError is now visible? If yes, is that sufficient to debug?

[Geethapranay1]

@fsimonis could you clarify what context you'd expect? I can catch the ModuleNotFoundError and re-raise it with the micro simulation path included, ex: Missing dependency 'foamlib' required by micro simulation 'micro' is that what you are expecting?

[fsimonis]

This is the output:

05/26/2026 11:06:04 AM - micro_manager.micro_manager - INFO - Total number of micro simulations: 100
Traceback (most recent call last):
  File ".../venv/bin/micro-manager-precice", line 8, in <module>
    sys.exit(main())
             ~~~~^^
  File ".../micro-manager/micro_manager/__init__.py", line 123, in main
    manager.initialize()
    ~~~~~~~~~~~~~~~~~~^^
  File ".../micro-manager/micro_manager/micro_manager.py", line 601, in initialize
    micro_problem_base = load_backend_class(self._config.get_micro_file_name())
  File ".../micro_manager/micro_simulation.py", line 602, in load_backend_class
    module = ipl.import_module(path_to_micro_file)
  File "/usr/lib/python3.14/importlib/__init__.py", line 88, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1406, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1371, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1342, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 938, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 759, in exec_module
  File "<frozen importlib._bootstrap>", line 491, in _call_with_frames_removed
  File ".../micro/python/micro.py", line 5, in <module>
    import foamlib
ModuleNotFoundError: No module named 'foamlib'

My propsed fix in #262 results in:

05/26/2026 11:08:51 AM - micro_manager.micro_manager - INFO - Total number of micro simulations: 100
Traceback (most recent call last):
  File "/.../micro_manager/micro_simulation.py", line 605, in load_backend_class
    mod = ipl.import_module(path_to_micro_file)
  File "/usr/lib/python3.14/importlib/__init__.py", line 88, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1406, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1371, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1342, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 938, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 759, in exec_module
  File "<frozen importlib._bootstrap>", line 491, in _call_with_frames_removed
  File "/.../micro/python/micro.py", line 5, in <module>
    import foamlib
ModuleNotFoundError: No module named 'foamlib'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/.../venv/bin/micro-manager-precice", line 8, in <module>
    sys.exit(main())
             ~~~~^^
  File "/.../micro-manager/micro_manager/__init__.py", line 123, in main
    manager.initialize()
    ~~~~~~~~~~~~~~~~~~^^
  File "/.../micro-manager/micro_manager/micro_manager.py", line 601, in initialize
    micro_problem_base = load_backend_class(self._config.get_micro_file_name())
  File "/.../micro_manager/micro_simulation.py", line 612, in load_backend_class
    raise RuntimeError(
        f"Counld not load a dependency of the python module '{path_to_micro_file}' containing the micro simulation: {ie}"
    )
RuntimeError: Counld not load a dependency of the python module 'python.micro' containing the micro simulation: No module named 'foamlib'

I'm fine with both.

[Geethapranay1]

@fsimonis thanks for testing this and sharing the comparison with #262, really helpful
The contextual messages are a good idea. I'll update my pr to add the wrapping and I'll keep it as ModuleNotFoundError with from chaining so we preserve the exception type and get a clean traceback. I already have tests covering the missing dependency cases too.

[IshaanDesai]

@Geethapranay1 I merged the solution proposed by @fsimonis. From your contribution, the tests could still be valuable. Can you please merge the upstream develop branch into your branch and then reformulate the tests?

[Geethapranay1]

@IshaanDesai Before I rebase the tests, i noted that on #262 error handling wrapping ModuleNotFoundError in RuntimeError drops the .name attribute and exception type, which means callers can't programmatically distinguish a missing dependency from other runtime failures may be re-raising as ModuleNotFoundError(...) from e preserves both the type and the causal chain while still adding the contextual message and also there is a minor typo error "Counld" -> "Could" typo on l623. i will include this fix alongside the tests and happy to take a opinion on the RuntimeError