Add an A2UI iframe and MCP catalogs #3157

Tracking issue for the iframe and MCP catalog.

What

Two A2UI v1.0 catalogs that embed untrusted web content in a sandboxed frame next to the basic catalog:

• catalogs/iframe/: WebAppFrameUrl and WebAppFrameSrcdoc, sandboxed frames that load an external URL or inline HTML and talk to the surface through a small message protocol (actions, data model paths, host functions).
• catalogs/mcp/: McpApp, which renders an MCP App resource through the MCP Apps JSON-RPC bridge, plus callMcpTool (the five data transformation functions move into the filesystem sample in refactor(catalogs): move the data functions from the MCP catalog into the filesystem sample #3171, resolving Split the data transformation functions out of the MCP catalog into a transformations catalog #3153).

Both are implemented as universal web components in @a2ui/catalog-iframe and @a2ui/catalog-mcp (typescript/catalogs/), registered next to the basic catalog; a surface created with the basic catalog selects them per component through catalogId.

Design points

• One sandbox implementation shared by both packages (typescript/catalogs/shared/sandbox/, copied into each package at build time so neither depends on the other): the double-iframe sandbox proxy the MCP Apps specification requires for web hosts. The outer frame is the proxy page, the inner frame holds the untrusted content without allow-same-origin. The proxy is served from the host origin by default and from a dedicated origin through configureSandbox({baseUrl}).
• configureMcpCatalog({getMcpClientForTool, processor, ...}) is the single host configuration call of the MCP catalog.
• Catalog schemas follow the v1.0 Catalog Schema Rules and are registered in specification/v1_0/test/run_tests.py; each example is exercised end to end by a Karma test in its package and rendered by the Lit, React and Angular explorers.

Pull requests (stack order)

1. [MCP] Add the v1 MCP catalog with the McpApp component schema #2945 MCP v1 catalog schema and McpApp specification (merged)
2. refactor(catalogs): move the data functions from the MCP catalog into the filesystem sample #3171 move the data functions from the MCP catalog into the filesystem sample (merged)
3. [MCP] Add the shared double-iframe sandbox and host helpers #3056 shared double-iframe sandbox and host helpers (merged)
4. [MCP] feat(catalog-mcp): configureMcpCatalog and the v1.0 entry point #3186 @a2ui/catalog-mcp: build tooling, configureMcpCatalog, v1.0 entry point, community samples on it
5. [MCP] Add the McpApp universal component and mcpCatalog to @a2ui/catalog-mcp` #2799 @a2ui/catalog-mcp: McpApp and mcpCatalog
6. [MCP] Add the 3D geometry MCP App example #3010 MCP examples, explorer integration, mock MCP server
7. [MCP] feat(samples): add the Kanban board showcase for agent and MCP App communication #3226 Kanban board showcase sample (samples/community/mcp/a2ui-kanban/)
8. [iFrame] Add the iframe catalog schema #2795 iframe catalog schema and examples
9. [iFrame] Add the @a2ui/catalog-iframe package and frame bridge #2797 @a2ui/catalog-iframe package and sandbox assets
10. [iFrame] Add the WebAppFrameUrl and WebAppFrameSrcdoc universal components #2798 WebAppFrameUrl and WebAppFrameSrcdoc components
11. [iFrame] Add the srcdoc tip calculator example to the iframe catalog #3008 srcdoc tip calculator example
12. [iFrame] Add the url order tracker example to the iframe catalog #3009 URL order tracker example
13. docs(site): add Iframe Catalog developer guide #2803 guide: iframe and MCP catalogs

Related

• Angular implementation for MCP App Component #673 Angular implementation for MCP App Component (precursor)
• Split the data transformation functions out of the MCP catalog into a transformations catalog #3153 Split the data transformation functions out of the MCP catalog (resolved by refactor(catalogs): move the data functions from the MCP catalog into the filesystem sample #3171)
• Clean up folder samples/community. #1698 publish @a2ui/catalog-mcp (community samples alias the monorepo build until then)