[marc-lehner]

On Windows the extension loads no nodes. rdkit_descriptors.py imports SA_Score and NP_Score from RDKit's Contrib directory, which it expected under <prefix>/share/RDKit/Contrib. conda puts it there on Linux and macOS, but under <prefix>/Library/share/RDKit/Contrib on Windows. The import fails, and with it the whole extension:

Failed to load extension org.rdkit.python_rdkit_nodes from src with error: ...
  File ".../src/rdkit_descriptors.py", line 62, in <module>
    import SA_Score
ModuleNotFoundError: No module named 'SA_Score'

The fix tries both layouts relative to sys.exec_prefix, then RDConfig.RDContribDir, the documented way to reach Contrib (see rdkit/rdkit#2279). RDConfig stores the prefix from install time, so it is only the fallback for an environment that was moved; rdkit.Chem.Descriptors already imports it. On Linux and macOS the first path is the one used so far, so nothing changes there.

Verified on Windows (KNIME Analytics Platform 5.12, RDKit 2025.09.6 from conda-forge):

• Without the fix, the extension's nodes are missing from the node repository and the error above is logged.
• With the fix, all 3 nodes load (Calculate All Descriptors, Get Parent Molecule, Stereoisomer Enumeration). The descriptor function returns all 219 values for aspirin, including NP_Score, and SA_Score loads from Library\share\RDKit\Contrib.

The same commit is in the knime-community fork for the release lines: knime-community#9 (master), knime-community#10 (releases/5.13) and knime-community#11 (releases/5.12).

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