Client asked for the raw footage and the prompt library. Where does the handoff line sit?

Retainer client of two years, video and social for a small brokerage, gave notice last month. Amicable. Then the request came in: all raw footage, the edit project files, the content calendar template, and the prompt library we built for their brand voice.

The footage I'll hand over without argument. They paid for the shoots, it's their properties and their people.

The prompt library is where I stopped. That's about forty hours of iteration by us, tuned to their voice but built on our own base structure that we use across seven accounts. Hand it over and I've handed a competitor's future vendor our method. The contract says work product delivered under the agreement belongs to the client, which was written in 2022 when work product meant finished videos. It doesn't define whether a prompt is work product or a tool.

There's a real argument that they paid for the forty hours inside the retainer, so it's theirs. There's an equally real argument that they bought outputs and the machinery isn't included, the way a photographer doesn't hand over lighting diagrams. I don't have a clean answer and I'm not going to litigate it over a two year account that ended well.

Any opinion on where the line sits is worth a specific lawyer conversation, since how a work product clause reads varies by state and by the actual wording. What I want is where operators think the line should sit before it hits the contract.