feat(channels): add streaming response hooks to ChannelBase

- Add onResponseChunk hook for progressive text display during streaming
- Add onResponseComplete hook for customizing response delivery
- Update mock plugin channel to support streaming chunks

This enables channels to display AI responses progressively as they stream,
improving user experience with real-time feedback.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/channels/base/src/ChannelBase.ts

@@ -72,6 +72,30 @@ export abstract class ChannelBase {
 
   onToolCall(_chatId: string, _event: ToolCallEvent): void {}
 
+  /**
+   * Called for each text chunk as the agent streams its response.
+   * Override to implement progressive display (e.g., updating an AI card in-place).
+   * Default: no-op (chunks are collected internally and delivered via onResponseComplete).
+   */
+  protected onResponseChunk(
+    _chatId: string,
+    _chunk: string,
+    _sessionId: string,
+  ): void {}
+
+  /**
+   * Called when the agent's full response is ready.
+   * Override to customize delivery (e.g., finalize an AI card).
+   * Default: calls sendMessage() with the full response text.
+   */
+  protected async onResponseComplete(
+    chatId: string,
+    fullText: string,
+    _sessionId: string,
+  ): Promise<void> {
+    await this.sendMessage(chatId, fullText);
+  }
+
   /**
    * Register a slash command handler. Subclasses can call this to add
    * platform-specific commands (e.g., /start for Telegram).
@@ -223,13 +247,25 @@ export abstract class ChannelBase {
     // pollution when concurrent messages hit the same session.
     const prev = this.sessionQueues.get(sessionId) ?? Promise.resolve();
     const current = prev.then(async () => {
-      const response = await this.bridge.prompt(sessionId, promptText, {
-        imageBase64: envelope.imageBase64,
-        imageMimeType: envelope.imageMimeType,
-      });
+      // Forward streaming chunks to the subclass hook
+      const onChunk = (sid: string, chunk: string) => {
+        if (sid === sessionId) {
+          this.onResponseChunk(envelope.chatId, chunk, sessionId);
+        }
+      };
+      this.bridge.on('textChunk', onChunk);
 
-      if (response) {
-        await this.sendMessage(envelope.chatId, response);
+      try {
+        const response = await this.bridge.prompt(sessionId, promptText, {
+          imageBase64: envelope.imageBase64,
+          imageMimeType: envelope.imageMimeType,
+        });
+
+        if (response) {
+          await this.onResponseComplete(envelope.chatId, response, sessionId);
+        }
+      } finally {
+        this.bridge.off('textChunk', onChunk);
       }
     });
     this.sessionQueues.set(