tl;dr: Inkwash is a browser-based watercolor sketching app built as a single HTML file using WebGL2, simulating pigment, water, and paper via stacked float textures and Stam's Stable Fluids algorithm. It models effects like chromatographic bleed, edge darkening, granulation, and Beer-Lambert light absorption to mimic real watercolor behavior, with a "fix" command that bakes wet pigment into the paper for layering. Notably, the author built the entire app by prompting Claude (Anthropic's unreleased "Fable 5" model) without writing code themselves, and the accompanying explainer is largely AI-generated.