refactor(core): Centralize tool response formatting (#743)

packages/core/src/utils/generateContentResponseUtilities.ts

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { GenerateContentResponse } from '@google/genai';
+import { GenerateContentResponse, Part } from '@google/genai';
 
 export function getResponseText(
   response: GenerateContentResponse,
@@ -15,3 +15,7 @@ export function getResponseText(
       .join('') || undefined
   );
 }
+
+export function getResponseTextFromParts(parts: Part[]): string | undefined {
+  return parts?.map((part) => part.text).join('') || undefined;
+}