There are some things that are on the fence in terms of materiality. For example, is the valuation pre- or post-money? Is there an option pool set aside?
Lastly, there are some types of agreements that cannot be done just on a handshake — there has to be a written agreement in order to be enforceable. IIRC from my law school days, this includes the sale of real estate and a contract that, by its terms, cannot be completed in a year. The latter excludes things that are known to take more than a year, like building a skyscraper. It would include "pet-sit my dog for 13 months while I'm vacationing", for example.
Breaking a contract is typically not breaking the law.
And there, something is enforced that is not the law but where you are lawfully obliged to a sanction afterwards ?
I don't really understand why you'd say that ? Isn't the law kind of saying "you shall not break contracts" ? And if it's not, what's the point of a contract ?
Regarding "breaking a contract": Contracts often stipulate penalties for non-performance of terms within them. For example, you contract with me to rent my house for 5 years. The contract stipulates that if you leave early, I am entitled to keep the deposit. In common language, people will refer to leaving early as "breaking the contract", but there is nothing illegal about doing so.
Regarding "illegal": If the contract does not specify some penalty for non-performance of a clause, or it does specify one but you somehow avoid the penalty, then it would become a matter for the courts, but importantly, it would be a civil court, not a criminal court. You have not broken a law, you have broken a contract, and the civil courts will determine how this situation will be made right.