Type Alias IndexRangeKeyOf<CF, IT>

IndexRangeKeyOf: CF extends { indexes?: infer I }
    ? I extends Record<string, unknown>
        ? IT extends keyof I
            ? I[IT] extends { rangeKey: infer RK } ? RK & string : never
            : never
        : never
    : never

Derive the index range-key token for a specific index token.

When CF carries an indexes object and IT is a member key, this extracts the concrete rangeKey token type.