Add MCP Apps (SEP-1865) support and playbook#2
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Server-side helpers for serving interactive HTML widgets that MCP hosts (Cursor, Claude, ...) render inline with tool results: - ui_extension_capability / add_ui_extension_capability! — advertise the io.modelcontextprotocol/ui extension in initialize - register_ui_resource! + MCPUIResource — ui:// resources with the text/html;profile=mcp-app mime type - ui_tool_meta — dual-written _meta (ui.resourceUri + ui/resourceUri) for cross-host compatibility, with model/app visibility control - ui_tool_content / embedded_ui_resource — embed the widget copy in tool results (required by hosts that do not fetch resources/read) - mcp_app_html + MCP_APP_BOOTSTRAP_JS — complete widget document builder with the ui/initialize handshake, initialized notification, automatic size-changed reporting (ResizeObserver), multi-channel render-data delivery with late-subscriber replay, and host tools/call proxying - protocol version negotiation: initialize now echoes a client-requested version when listed in the new supported_protocol_versions config MCP-App-playbook.md documents the full requirement set, verification runbook (curl + standalone widget harness + Cursor), troubleshooting table, and a porting checklist for new applications. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…stays valid Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…widgets Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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What
First-class server-side support for MCP Apps (SEP-1865, extension
io.modelcontextprotocol/ui) — interactive HTML widgets that hosts like Cursor and Claude render inline with tool results — plusMCP-App-playbook.md, an end-to-end guide distilled from getting a production integration rendering in Cursor.New API (
src/apps.jl)ui_extension_capability()/add_ui_extension_capability!— advertise the Apps extension ininitializeregister_ui_resource!+MCPUIResource—ui://resources with thetext/html;profile=mcp-appmime typeui_tool_meta— dual-written_meta(ui.resourceUriandui/resourceUri) for cross-host compat, with model/app visibilityui_tool_content/embedded_ui_resource— embed the widget in tool results (hosts like Cursor render the embedded copy and don't fetchresources/read)mcp_app_html+MCP_APP_BOOTSTRAP_JS— complete widget document builder:ui/initializehandshake (protocolVersion/appInfo/appCapabilities),ui/notifications/initialized, automaticsize-changedvia ResizeObserver, multi-channel render-data delivery with late-subscriber replay, andtools/callproxying viawindow.mcpAppProtocol version negotiation
initializepreviously ignored the client's requestedprotocolVersion. Newsupported_protocol_versionsconfig lists additional versions the server will echo back when requested (default behavior unchanged).Tests
New
MCP Appstestset (50 assertions): capability shapes, meta dual-write, negotiation, HTML shell guards, and a full wire-level widget-backed server exercised through the package's own HTTP client (initialize → tools/list → resources/read → tools/call with embedded resource + structuredContent).🤖 Generated with Claude Code