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

packages/ai/src/providers/openai-completions.ts

@@ -127,6 +127,9 @@ export const streamOpenAICompletions: StreamFunction<"openai-completions", OpenA
 			};
 
 			for await (const chunk of openaiStream) {
+				// OpenAI documents ChatCompletionChunk.id as the unique chat completion identifier,
+				// and each chunk in a streamed completion carries the same id.
+				output.responseId ||= chunk.id;
 				if (chunk.usage) {
 					output.usage = parseChunkUsage(chunk.usage, model);
 				}