Legal Question in Technology Law in California

If the agreement were only for diagnostics, he should have consulted you before taking the next step. That said, though, you may be fortunate that he salvaged your work. If he's a friend who obviously cared about you to protect your work, you should try to work out a reasonable solution.

I agree. This reminds me of a case we all studied in law school on the subject of implied contracts. In the case, a guy is hit by a streetcar, and is lying, unconscious and bleeding, in the street. A medical doctor happens to be walking by and notices the accident. He binds the victim's wounds and keeps him from dying. A month later, when the victim is much better, the doc sends the victim a bill. The victim refuses to pay on the ground that he had no contract with the doctor. It goes to court and the doctor gets a judgment for the fair value of his services to the victim. This illustrates the principle of a "quasi-contract" or "contract implied in law," both topics you can research at length on Google.