Build self-contained, double-click-to-open HTML prototypes so the user can vet an interface before it gets built. One file holds several structurally different variants of a page, app screen, component, flow, or terminal/TUI layout (rendered in-browser), plus a draggable Design Deck for flipping between variants, tuning fonts, colors, spacing, shape, motion and 'feel' with live dials, trying vibe presets, checking viewport sizes and light/dark, pinning comments on elements, and an 'Export to LLM' button that copies the chosen variant and every dial value as a handoff block to paste back to the agent. Use this whenever the user wants to prototype, mock up, wireframe, explore options for, or sanity-check a UI (landing page, dashboard, settings page, onboarding, form, mobile screen, component, CLI/TUI layout), or says 'what should this look like', 'show me a few options', 'let me tweak it before we build', 'vet the design'. Also use it when the user pastes a block starting with 'AI-ASSIST