fix(lit): handle TextPart fallback messages in shell and contact sample clients

samples/client/lit/contact/client.ts

@@ -32,6 +32,11 @@ type A2AServerPayload =
 
 import { componentRegistry } from "@a2ui/lit/ui";
 
+export interface A2UIClientResponse {
+  messages: v0_8.Types.ServerToClientMessage[];
+  fallbackText: string | null;
+}
+
 export class A2UIClient {
   #ready: Promise<void> = Promise.resolve();
   get ready() {
@@ -40,7 +45,7 @@ export class A2UIClient {
 
   async send(
     message: v0_8.Types.A2UIClientEventMessage
-  ): Promise<v0_8.Types.ServerToClientMessage[]> {
+  ): Promise<A2UIClientResponse> {
     const catalog = componentRegistry.getInlineCatalog();
     const finalMessage = {
       ...message,
@@ -59,15 +64,24 @@ export class A2UIClient {
     if (response.ok) {
       const data = (await response.json()) as A2AServerPayload;
       const messages: v0_8.Types.ServerToClientMessage[] = [];
+      const textParts: string[] = [];
       if ("error" in data) {
         throw new Error(data.error);
       } else {
         for (const item of data) {
-          if (item.kind === "text") continue;
-          messages.push(item.data);
+          if (item.kind === "text") {
+            textParts.push(item.text);
+          } else {
+            messages.push(item.data);
+          }
         }
       }
-      return messages;
+      return {
+        messages,
+        fallbackText: messages.length === 0 && textParts.length > 0
+          ? textParts.join('\n')
+          : null,
+      };
     }
 
     const error = (await response.json()) as { error: string };

samples/client/lit/contact/contact.ts

@@ -26,7 +26,7 @@ import {
 } from "lit";
 import { customElement, state } from "lit/decorators.js";
 import { theme as uiTheme } from "./theme/theme.js";
-import { A2UIClient } from "./client.js";
+import { A2UIClient, type A2UIClientResponse } from "./client.js";
 import {
   SnackbarAction,
   SnackbarMessage,
@@ -377,9 +377,11 @@ export class A2UIContactFinder extends SignalWatcher(LitElement) {
 
   async #sendAndProcessMessage(request: v0_8.Types.A2UIClientEventMessage) {
     this.#requesting = true;
-    const messages = await this.#sendMessage(request);
+    this.#error = null;
+    const { messages, fallbackText } = await this.#sendMessage(request);
 
     this.#lastMessages = messages;
+    this.#error = fallbackText;
 
     // this.#processor.clearSurfaces(); // Removed to allow partial updates
     this.#processor.processMessages(messages);
@@ -394,7 +396,7 @@ export class A2UIContactFinder extends SignalWatcher(LitElement) {
 
   async #sendMessage(
     message: v0_8.Types.A2UIClientEventMessage
-  ): Promise<v0_8.Types.ServerToClientMessage[]> {
+  ): Promise<A2UIClientResponse> {
     try {
       this.#requesting = true;
       const response = await this.#a2uiClient.send(message);
@@ -408,7 +410,7 @@ export class A2UIContactFinder extends SignalWatcher(LitElement) {
       this.#requesting = false;
     }
 
-    return [];
+    return { messages: [], fallbackText: null };
   }
 
   snackbar(

samples/client/lit/shell/app.ts

@@ -26,7 +26,7 @@ import {
 } from "lit";
 import { customElement, state } from "lit/decorators.js";
 import { theme as uiTheme } from "./theme/default-theme.js";
-import { A2UIClient } from "./client.js";
+import { A2UIClient, type A2UIClientResponse } from "./client.js";
 import {
   SnackbarAction,
   SnackbarMessage,
@@ -407,12 +407,11 @@ export class A2UILayoutEditor extends SignalWatcher(LitElement) {
 
   async #sendMessage(
     message: v0_8.Types.A2UIClientEventMessage
-  ): Promise<v0_8.Types.ServerToClientMessage[]> {
+  ): Promise<A2UIClientResponse> {
     try {
       this.#requesting = true;
       this.#startLoadingAnimation();
-      const response = this.#a2uiClient.send(message);
-      await response;
+      const response = await this.#a2uiClient.send(message);
       this.#requesting = false;
       this.#stopLoadingAnimation();
 
@@ -424,7 +423,7 @@ export class A2UILayoutEditor extends SignalWatcher(LitElement) {
       this.#stopLoadingAnimation();
     }
 
-    return [];
+    return { messages: [], fallbackText: null };
   }
 
   #maybeRenderData() {
@@ -511,11 +510,13 @@ export class A2UILayoutEditor extends SignalWatcher(LitElement) {
   }
 
   async #sendAndProcessMessage(request) {
-    const messages = await this.#sendMessage(request);
+    this.#error = null;
+    const { messages, fallbackText } = await this.#sendMessage(request);
 
     console.log(messages);
 
     this.#lastMessages = messages;
+    this.#error = fallbackText;
     this.#processor.clearSurfaces();
     this.#processor.processMessages(messages);
   }

samples/client/lit/shell/client.ts

@@ -20,6 +20,11 @@ import { v0_8 } from "@a2ui/lit";
 
 const A2UI_MIME_TYPE = "application/json+a2ui";
 
+export interface A2UIClientResponse {
+  messages: v0_8.Types.ServerToClientMessage[];
+  fallbackText: string | null;
+}
+
 export class A2UIClient {
   #serverUrl: string;
   #client: A2AClient | null = null;
@@ -54,7 +59,7 @@ export class A2UIClient {
 
   async send(
     message: v0_8.Types.A2UIClientEventMessage | string
-  ): Promise<v0_8.Types.ServerToClientMessage[]> {
+  ): Promise<A2UIClientResponse> {
     const client = await this.#getClient();
 
     let parts: Part[] = [];
@@ -99,14 +104,22 @@ export class A2UIClient {
     const result = (response as SendMessageSuccessResponse).result as Task;
     if (result.kind === "task" && result.status.message?.parts) {
       const messages: v0_8.Types.ServerToClientMessage[] = [];
+      const textParts: string[] = [];
       for (const part of result.status.message.parts) {
         if (part.kind === 'data') {
           messages.push(part.data as v0_8.Types.ServerToClientMessage);
+        } else if (part.kind === 'text') {
+          textParts.push(part.text);
         }
       }
-      return messages;
+      return {
+        messages,
+        fallbackText: messages.length === 0 && textParts.length > 0
+          ? textParts.join('\n')
+          : null,
+      };
     }
 
-    return [];
+    return { messages: [], fallbackText: null };
   }
 }