canvas

The canvas worker stores diagrams as editable source. A canvas is a named record — mermaid text, or an excalidraw scene JSON for a freeform whiteboard — kept under a stable 8-character id. The worker never renders anything; the console does the drawing, so a canvas::* call appears in chat as the live diagram and the canvas page lists and edits everything stored. The source is the artifact, which is what keeps a diagram editable instead of frozen into pixels.

Ids are stable across updates on purpose: revise a diagram as the conversation evolves and every earlier reference to it keeps working. Records persist in the state worker, so nothing is lost across a restart.

Mermaid should not be written from memory. canvas::syntax returns the families the renderer actually supports with a working example each, and canvas::validate parses source without storing it — together they mean a broken diagram never lands in the store or renders as an error card.