napkin
A design canvas where every artboard is a real React file, and an agent edits it with you.
The target: an agent and I edit one component on a canvas at once, and the result is a real component file on disk. In the spikes, the two-cursor demo runs; it is not a product and I have not used it for real work.
The spikes are small on purpose and live in separate checkouts. The spec borrows a short list of invariants from my earlier precision-canvas repo and leaves the rest of it behind.
I learned to start from the file format, because files on disk stay the source of truth.