Function unit_signature_for 

pub fn unit_signature_for(
    name: &str,
    table: &UnitTable,
    combined_types: HashMap<String, Arc<TypeDecl>>,
) -> UnitSignature

Builds a UnitSignature for name from table, reusing combined_types (typically a fresh combined_types_for(name, ..) call, mirrored here as a parameter rather than recomputed so a caller building both alongside each other pays for one traversal, not two).

Every category below is a direct, field-by-field projection off UnitTable’s own real shapes — see this module’s own doc comment and design/tracks/incrementality.md §3.4 (Q4) for which fields are excluded and why.