fix(ai): strip partialJson from responses tool calls

Mutate persisted tool-call blocks in place on function_call completion,
remove partialJson, and emit the same reference on toolcall_end.
Add regression coverage for persisted block cleanup and event identity.

fixes #3078

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

@@ -116,7 +116,11 @@ export const streamOpenAIResponses: StreamFunction<"openai-responses", OpenAIRes
 			stream.push({ type: "done", reason: output.stopReason, message: output });
 			stream.end();
 		} catch (error) {
-			for (const block of output.content) delete (block as { index?: number }).index;
+			for (const block of output.content) {
+				delete (block as { index?: number }).index;
+				// partialJson is only a streaming scratch buffer; never persist it.
+				delete (block as { partialJson?: string }).partialJson;
+			}
 			output.stopReason = options?.signal?.aborted ? "aborted" : "error";
 			output.errorMessage = error instanceof Error ? error.message : JSON.stringify(error);
 			stream.push({ type: "error", reason: output.stopReason, error: output });