Add AppBridge.sendHostContextChange + reexport RESOURCE_URI_META_KEY (#87)

* Export  RESOURCE_URI_META_KEY from app-bridge

* add sendHostContextChange

* nit

src/app-bridge.ts

@@ -60,6 +60,7 @@ import {
   McpUiSizeChangedNotificationSchema,
 } from "./types";
 export * from "./types";
+export { RESOURCE_URI_META_KEY } from "./app";
 export { PostMessageTransport } from "./message-transport";
 
 /**
@@ -153,8 +154,8 @@ type RequestHandlerExtra = Parameters<
  */
 export class AppBridge extends Protocol<Request, Notification, Result> {
   private _appCapabilities?: McpUiAppCapabilities;
+  private _hostContext: McpUiHostContext = {};
   private _appInfo?: Implementation;
-  private _hostContext: McpUiHostContext;
 
   /**
    * Create a new AppBridge instance.
@@ -625,13 +626,23 @@ export class AppBridge extends Protocol<Request, Notification, Result> {
     }
     if (hasChanges) {
       this._hostContext = hostContext;
-      this.notification((<McpUiHostContextChangedNotification>{
-        method: "ui/notifications/host-context-changed",
-        params: changes,
-      }) as Notification); // Cast needed because McpUiHostContext is a params type that doesn't allow arbitrary keys.
+      this.sendHostContextChange(changes);
     }
   }
 
+  /**
+   * Send a host context change notification to the app.
+   * Only sends the fields that have changed (partial update).
+   */
+  sendHostContextChange(
+    params: McpUiHostContextChangedNotification["params"],
+  ): Promise<void> | void {
+    return this.notification((<McpUiHostContextChangedNotification>{
+      method: "ui/notifications/host-context-changed",
+      params,
+    }) as Notification);
+  }
+
   /**
    * Send complete tool arguments to the Guest UI.
    *

src/app.ts

@@ -41,7 +41,7 @@ import {
 } from "./types";
 import { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";
 
-export { PostMessageTransport } from "./message-transport.js";
+export { PostMessageTransport } from "./message-transport";
 export * from "./types";
 
 /**