The ProtoID field in BondRef was misleading as it could hold both proto IDs (from proto+proto bonds) and molecule IDs (from mol+mol bonds). Rename to SourceID with updated JSON tag to better reflect its purpose. Changes: - Rename BondRef.ProtoID to SourceID in types.go - Update JSON tag from proto_id to source_id - Update all usages in mol_bond.go and tests 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>