Add double-connect guard to prevent protocol message handling errors

src/app-bridge.test.ts

@@ -615,6 +615,40 @@ describe("App <-> AppBridge integration", () => {
     });
   });
 
+  describe("double-connect guard", () => {
+    it("AppBridge.connect() throws if already connected", async () => {
+      await bridge.connect(bridgeTransport);
+      await app.connect(appTransport);
+
+      // Attempting to connect again with a different transport should throw
+      const [, secondBridgeTransport] = InMemoryTransport.createLinkedPair();
+      await expect(bridge.connect(secondBridgeTransport)).rejects.toThrow(
+        "AppBridge is already connected",
+      );
+    });
+
+    it("App.connect() throws if already connected", async () => {
+      await bridge.connect(bridgeTransport);
+      await app.connect(appTransport);
+
+      // Attempting to connect again should throw
+      const [secondAppTransport] = InMemoryTransport.createLinkedPair();
+      await expect(app.connect(secondAppTransport)).rejects.toThrow(
+        "App is already connected",
+      );
+    });
+
+    it("AppBridge.connect() throws even when called with the same transport", async () => {
+      await bridge.connect(bridgeTransport);
+      await app.connect(appTransport);
+
+      // Should throw regardless of whether it's the same or a different transport
+      await expect(bridge.connect(bridgeTransport)).rejects.toThrow(
+        "AppBridge is already connected",
+      );
+    });
+  });
+
   describe("ping", () => {
     it("App responds to ping from bridge", async () => {
       await bridge.connect(bridgeTransport);

src/app-bridge.ts

@@ -1409,6 +1409,11 @@ export class AppBridge extends Protocol<
    * ```
    */
   async connect(transport: Transport) {
+    if (this.transport) {
+      throw new Error(
+        "AppBridge is already connected. Call close() before connecting again.",
+      );
+    }
     if (this._client) {
       // When a client was passed to the constructor, automatically forward
       // MCP requests/notifications between the view and the server

src/app.ts

@@ -1112,6 +1112,11 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
     ),
     options?: RequestOptions,
   ): Promise<void> {
+    if (this.transport) {
+      throw new Error(
+        "App is already connected. Call close() before connecting again.",
+      );
+    }
     await super.connect(transport);
 
     try {