There is undocumented but there are two ways you can call contract method

One by transaction other by query. The transaction contract call has the session and is used to mutate the state but it does not allow return values

Other call method is http query which allows return value

Allow both options, currently we only allow transaction contract call

Why we need this change:

Only http query allows return values for the functions so we need this functionality in order to test the deployed contracts
because rusk-wallet allows deploying contracts