- Add +1 safety margin to grid_radius to handle banker's rounding at cell
boundaries in the spatial index
- Move symbol property guards inside per-symbol try/except to prevent
AttributeError from aborting all pin processing
- Replace O(n) connected_points scan for pin matching with spatial index
lookup (_frontier_has_neighbour), consistent with flood-fill approach
- Wrap float(x)/float(y) conversion with clear user-facing error message
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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