Module registry 

Type registry for tracking user-defined types during parsing.

The registry stores type definitions discovered during the discovery pass and provides lookup during parsing and code generation. It supports:

• Primitives: Nat, Int, Text, Bool (built-in)
• Structs: Named records with typed fields
• Enums: Sum types with variants (unit or tuple)
• Generics: Parameterized types (List of T, Pair of T and U)

The registry is populated by super::DiscoveryPass before main parsing begins.

Structs

FieldDef

Field definition within a struct

TypeRegistry

VariantDef

Phase 33: Variant definition for sum types

Enums

FieldType

Type reference for struct fields (avoids circular deps with ast::TypeExpr)

TypeDef