[AI-stack FB6] @netscript/fresh-ui: interactive MCP-App bridge (widget-action → tools/call → re-render, deferred)

[rickylabs]

Summary (deferred — post-v1)

The interactive MCP-App bridge in @netscript/fresh-ui: the bidirectional half deferred out of FB4 (#257). A rendered MCP-UI widget can dispatch an action → tools/call → the host re-renders the widget with the new resource, all without a full round-trip through a new connection.

Load-bearing gotcha (★)

Hand the new resource to the EXISTING AppBridge — never call connect() again. A second connect() throws "AppBridge is already connected". The bridge is connect-once / update-many against a streaming host: one connection, many resource updates.

• Sandbox stays allow-scripts only (no allow-same-origin) — the widget is untrusted.
• Depends on the MCP tool-call plumbing (E5, [AI-stack E5] @netscript/ai: McpTransportPort (stdio + reconnectable Streamable-HTTP + auth modes) #244) and the one-way render widget (FB4, [AI-stack FB4] fresh-ui: mcp-ui-widget (themed sandboxed ui:// iframe) #257).

Scope

@netscript/fresh-ui MCP-UI seam (bidirectional). wave:defer (post-v1, after FB4). POC reference: eis-chat #57 (lib/mcp.ts#L78-104 + mcp-widget.tsx#L185-195).

Part of #238 · Refs #244 (E5) #257 (FB4) · POC eis-chat#57