Block registry

Status: planned — the highest-leverage Arco milestone.

The block registry replaces implicit type unions and giant render switches with one manifest per block.

defineBlock() contract

Each block exports:

Field	Purpose
type	Stable string identifier
schema	Zod schema → runtime validation + JSON Schema
description	Prompt text for the AI
adaptivity	Size classes, input profiles, reflow rules
examples	Golden samples for prompts, docs, and tests
render	(props) => ReactNode mapping

Contract outputs (from one definition)

1. Runtime validation — reject or repair malformed output before render
2. JSON Schema / grammar — constrained decoding and tool arguments
3. System prompt — generated vocabulary, never hand-maintained
4. Design catalog — Storybook-style docs from examples
5. Render mapping — registry[type].render

Two renderers, one registry

Path	Input	Use case
Streaming	OpenUI Lang / A2UI	Chat inline blocks
Static	Block JSON	Durable apps, dashboards

Both resolve through registry[type].render.

Adaptivity descriptor

Blocks declare how they reflow across window size classes:

adaptivity: {
  inputProfiles: ["pointer", "touch"],
  minWidth: 220,
  idealColumns: { compact: 1, medium: 2, expanded: 4 },
  onCompact: "stack",
}

Size classes use CSS container queries — Compact / Medium / Expanded — not device types.

Roadmap phase

This is the Now phase in the Arco spec:

• Registry + Zod for existing blocks
• Generated system prompt from registry
• Runtime validation + repair
• OpenUI spike: two block types end-to-end
• Design System workspace as living catalog

See the Arco spec overview for the full roadmap.