Renderer Rules

renderer/ draws the current ImageDocument plus read-only editor overlays.
Rendering backend details, e.g. WebGL objects, stay isolated here.
Do not mutate document or editor state directly.
Renderer interactions may emit intents/events only; callers translate them into commands.
Do not import React components or view code.
Do not leak backend objects into core/, commands/, editor/, or React state.
Cache only derived rendering data; authoritative state lives in core/ and editor/.