refactor(acp): migrate to @agentclientprotocol/sdk and clean up handlers

- Replace deprecated ACP session manager with new SDK integration
- Add acpFileHandler test coverage
- Remove obsolete acpMessageHandler and acpSessionManager
- Update type definitions and connection handlers
- Apply code formatting fixes

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

packages/cli/src/acp-integration/acpAgent.ts

@@ -214,7 +214,16 @@ class QwenAgent implements Agent {
     }
 
     await this.createAndStoreSession(config, sessionData.conversation);
-    return null as unknown as LoadSessionResponse;
+
+    const modesData = this.buildModesData(config);
+    const availableModels = this.buildAvailableModels(config);
+    const configOptions = this.buildConfigOptions(config);
+
+    return {
+      modes: modesData,
+      models: availableModels,
+      configOptions,
+    };
   }
 
   async unstable_listSessions(
@@ -323,6 +332,13 @@ class QwenAgent implements Agent {
     await session.cancelPendingPrompt();
   }
 
+  async extMethod(
+    method: string,
+    _params: Record<string, unknown>,
+  ): Promise<Record<string, unknown>> {
+    throw RequestError.methodNotFound(method);
+  }
+
   // --- private helpers ---
 
   private async newSessionConfig(