artifact-capabilities

# Artifact runtime capabilities A published Artifact page can declare **runtime capabilities** — abilities the claude.ai viewer grants the page at open time — by passing `capabilities: {name: config}` to the Artifact tool. The control plane is the authority on valid names and config shapes. Declaration gestures: **omitting** `capabilities` on a redeploy carries the stored declaration forward unchanged (and preserves the artifact's stored contract pin); an **empty object** `{}` is the explicit clear-all; a **non-empty object** is a full-set declaration (anything stored but not restated is revoked). Moving a republished artifact's runtime version is a deliberate gesture — pass `contract: 'latest'` to upgrade, or a specific version to pin or roll back — never a side effect of editing. **Available capabilities:** `artifact`, `downloads`, `mcp`, `self` — the complete set of capability names you may declare. Anything not listed is unavailable to this user. Runtime contract 0.2.21 Capability namespaces live behind `claude.use(name)`: `const db = await claude.use("db")` resolves the capability's namespace, or `null` when this view cannot run it (not served, not granted, or failed to load — indistinguishable by design). Branch on `null` and design for absence. `window.claude` carries only `use`: no `window.claude.db`, `.room`, or `.artifact` member is ever promised, so never read one — render the page without them and light features up when the promise resolves (later, never with...