What are 'Const Type Parameters' and how do they impact API design?

Const type parameters (TS 5.0+) allow generic functions to infer literal and readonly types from arguments without manual assertions.

Usually, TypeScript 'widens' types when passed to generics (e.g., a literal 'red' becomes 'string'). Previously, developers had to use 'as const' at the call site. By adding 'const' to a generic parameter definition, the function caller gets 'as const'-like inference automatically. This is vital for builders and configuration functions where the exact literal values are needed for subsequent type-level logic.