If you have ever had any thoughts as to why it is critical to clarify the equity / IP position when you start working on something and why founder vesting is crucial, then please read this story of the SnapChat founder cluster fuck:
I think there are three points here that really matter:
1) The equity position in a new company needs to be clear from day one.
2) All founders must have founder vesting and good leaver / bad leaver provisions from day one.
3) All IP needs to be assigned to that company from day one.
Now, how realistic is it that this will happen on day one? Not very much. However, unless those three points are clear, you will have significant risk in your business that you will have to tidy up sooner or later.
Strikes me that some law firm should publish basic papers that founders can fill in to have a fundamental working relationship and so that these things can’t happen.