Project coding style

Follow the existing Racket style demonstrated in library-factory.rkt.
Use define primarily for module definitions, class state, and methods.
Use let and let* for method-local values and keep related operations in the same lexical scope.
Prefer explicit intermediate names, such as maker-key, when they clarify intent.
Keep implementations small and direct; avoid unnecessary helper layers.
Validate each invariant in one appropriate place. Do not duplicate constructor checks in callers or deserializers.
Use check/c and check/c* from utils.rkt for concise argument validation where validation is needed.
Preserve the surrounding formatting and naming style when modifying existing code.