When Claude publishes an artifact (a generated document, app, or file shown alongside the conversation) that writes to a store, it now recognizes a new "mcp" store-write kind alongside the existing "data" and "write_db" kinds, with its own instruction text for the model.
Separately, for artifacts that can respond live to comments, there's now a "durable_declined" result: this covers the case where a request to let Claude reply to comments was asked for but not approved, distinct from the existing "durable_refused" case where the server itself rejected it.
The added "mcp" kind lets artifacts write through MCP (Model Context Protocol, a way for Claude to connect to external tools and services) connections, and the new "durable_declined" state gives a clearer, more specific message when a live-reply request simply wasn't approved rather than being rejected by the server.