Legal Question in Business Law in California

You say "licensed handyman." There is no such thing as a handyman license in CA. The work this person did requires a contractor's license issued by the CA Contractor's State License Board. If he does not have either a Class B general contractor's license, or a carpentry subcontractor's license, he has committed a crime (thought they'll never bother to prosecute) and by law you do not owe him a single penny for the work. The written contract is irrelevant.

If he does hold a valid contractor's license, then the written document is irrelevant and voidable at your option due to being provided after the fact and unsigned. What you owe is the "reasonable value of the goods and services" provided at your request. How much that is, is either up to the two of you to work out, or you can refuse to pay him and let a small claims judge to decide.

I assume that although you refer to the guy as a "licensed handyman," he indeed has a valid contractor's license. If so, you may or may not owe the full contract price, but for sure you owe the "fair value" of the materials and labor provided, whether or not there is a complete valid written contract, under the "quantum meruit" legal theory, meaning a businessperson who provides a requested benefit is entitled to the fair value thereof. As a practical matter, and assuming the guy has a license for what he did, your best bet is to negotiate with him, starting with him furnishing some details as to the cost of materials used and the number of hours and his rate per hour. Maybe he'd rather settle for less than have to sue you. Also, it's uncertain whether he'd resort to the courts.