Multi-field variants use Enum_Variant_Payload nested types (avoids tag name clash).
Sema resolves data.Variant.Variant_i; enum field types fully resolve tuples.
Selfhost parses full type exprs in enum payloads; emit structs/tuples before enums.
Example: examples/nested_patterns.bux (Pair::Two, Box::Val((a,c)), Shape::Dot).
