Type Alias Schema

Recursive schema definition accepted by parse/safeParse/checkStructure. Each key can be a type-name string (with optional ? suffix and | unions), an array describing element type, a nested schema, or a Validator<T> function.

Note: the array slot accepts any-length arrays at the type level so that schemas declared as plain const variables (without as const) still satisfy the constraint. The runtime requires exactly one element and will surface a clear error message otherwise.