Fix analysis crash when SASA atom selection is empty - Small molecule example

[juliocesar-io]

Fix analysis crash: ValueError: Coordinates are empty in get_delta_sasa()

• Fixes: SASA computation fails in analysis step for example inputs (Coordinates are empty) #166

Problem

Running boltzgen run example/small_molecule_from_file_and_smiles/4g37.yaml --protocol protein-anything on v0.2.0 can fail in step 5/6: analysis:

• ValueError: Coordinates are empty (Biotite sasa())

Root cause

boltzgen/task/analyze/analyze_utils.py:get_delta_sasa() calls Biotite sasa() on an atom selection that can be empty for some inputs, which Biotite rejects.

Fix

File: boltzgen/task/analyze/analyze_utils.py

• Catch ValueError from the sasa(target_atoms, ...) call and return (nan, nan, nan) for the SASA metrics instead of aborting the pipeline.

Behavior change

• Pipeline no longer crashes in analysis.
• SASA-related metrics become NaN when the SASA selection is empty.

Test

boltzgen run example/small_molecule_from_file_and_smiles/4g37.yaml \
  --output workbench \
  --protocol protein-anything \
  --num_designs 2