fix(ai): expose provider response ids on assistant messages fixes #2245

packages/ai/src/providers/google.ts

@@ -86,6 +86,9 @@ export const streamGoogle: StreamFunction<"google-generative-ai", GoogleOptions>
 			const blocks = output.content;
 			const blockIndex = () => blocks.length - 1;
 			for await (const chunk of googleStream) {
+				// @google/genai documents GenerateContentResponse.responseId as an output-only field
+				// used to identify each response. Keep the first non-empty one from the stream.
+				output.responseId ||= chunk.responseId;
 				const candidate = chunk.candidates?.[0];
 				if (candidate?.content?.parts) {
 					for (const part of candidate.content.parts) {