[goose2] MCP Apps: translate ACP host capabilities into MCP initialization (#8623)

Signed-off-by: Andrew Harvard <aharvard@squareup.com>

ui/goose2/src/shared/api/acpConnection.ts

@@ -1,5 +1,9 @@
 import { invoke } from "@tauri-apps/api/core";
-import { GooseClient } from "@aaif/goose-sdk";
+import {
+  DEFAULT_GOOSE_MCP_HOST_CAPABILITIES,
+  GooseClient,
+  type GooseInitializeRequest,
+} from "@aaif/goose-sdk";
 import {
   PROTOCOL_VERSION,
   type Client,
@@ -7,6 +11,7 @@ import {
   type RequestPermissionRequest,
   type RequestPermissionResponse,
 } from "@agentclientprotocol/sdk";
+import packageJson from "../../../package.json";
 import { createWebSocketStream } from "./createWebSocketStream";
 import { perfLog } from "@/shared/lib/perfLog";
 
@@ -81,12 +86,18 @@ async function initializeConnection(): Promise<GooseClient> {
   const tInit = performance.now();
   await client.initialize({
     protocolVersion: PROTOCOL_VERSION,
-    clientCapabilities: {},
-    clientInfo: {
-      name: "goose2",
-      version: "0.1.0",
+    clientCapabilities: {
+      _meta: {
+        goose: {
+          mcpHostCapabilities: DEFAULT_GOOSE_MCP_HOST_CAPABILITIES,
+        },
+      },
     },
-  });
+    clientInfo: {
+      name: packageJson.name,
+      version: packageJson.version,
+    },
+  } satisfies GooseInitializeRequest);
   perfLog(
     `[perf:conn] client.initialize in ${(performance.now() - tInit).toFixed(1)}ms (total ${(performance.now() - tStart).toFixed(1)}ms)`,
   );

ui/pnpm-lock.yaml

@@ -648,6 +648,9 @@ importers:
 
   sdk:
     dependencies:
+      '@modelcontextprotocol/ext-apps':
+        specifier: ^0.3.1
+        version: 0.3.1(@modelcontextprotocol/sdk@1.27.1(zod@3.25.76))(react-dom@19.2.4(react@19.2.4))(react@19.2.4)(zod@3.25.76)
       zod:
         specifier: ^3.25.76
         version: 3.25.76

ui/sdk/package.json

@@ -40,6 +40,7 @@
     "format": "prettier --write src/"
   },
   "dependencies": {
+    "@modelcontextprotocol/ext-apps": "^0.3.1",
     "zod": "^3.25.76"
   },
   "peerDependencies": {

ui/sdk/src/index.ts

@@ -2,6 +2,7 @@ export * from "./generated/types.gen.js";
 export * from "./generated/zod.gen.js";
 export { GooseClient } from "./goose-client.js";
 export { createHttpStream } from "./http-stream.js";
+export * from "./mcp-apps.js";
 
 export {
   ClientSideConnection,

ui/sdk/src/mcp-apps.ts

@@ -0,0 +1,36 @@
+import type {
+  Implementation,
+  InitializeRequest,
+} from "@agentclientprotocol/sdk";
+import { RESOURCE_MIME_TYPE } from "@modelcontextprotocol/ext-apps";
+
+export const GOOSE_MCP_UI_EXTENSION_ID = "io.modelcontextprotocol/ui" as const;
+
+export interface GooseMcpUiExtensionSettings {
+  mimeTypes: string[];
+}
+
+export interface GooseMcpHostCapabilities {
+  extensions: Record<string, GooseMcpUiExtensionSettings>;
+}
+
+export interface GooseClientMeta {
+  goose: {
+    mcpHostCapabilities: GooseMcpHostCapabilities;
+  };
+}
+
+export type GooseInitializeRequest = InitializeRequest & {
+  clientCapabilities: NonNullable<InitializeRequest["clientCapabilities"]> & {
+    _meta: GooseClientMeta;
+  };
+  clientInfo: Implementation;
+};
+
+export const DEFAULT_GOOSE_MCP_HOST_CAPABILITIES: GooseMcpHostCapabilities = {
+  extensions: {
+    [GOOSE_MCP_UI_EXTENSION_ID]: {
+      mimeTypes: [RESOURCE_MIME_TYPE],
+    },
+  },
+};