Execution API defines InitChain method, which takes genesis time, genesis block height and chain ID as params.
This parameters are usually a part of genesis file, which is implementation specific.

To resolve this issue there are multiple options:

1. Create rollkit-specific "genesis" file.
2. Add this to rollkit config / command line options.
3. Add a method in Execution API for parsing those options from genesis file.

Option 1 & 2 are fragile and require node operators to keep duplicated configuration in sync.