fix(ai): disable OpenAI reasoning where supported

packages/ai/test/openai-responses-copilot-provider.test.ts

@@ -91,6 +91,80 @@ describe("openai-responses provider defaults", () => {
 		});
 	});
 
+	it.each(["gpt-5.1", "gpt-5.2", "gpt-5.3-codex", "gpt-5.4", "gpt-5.4-mini", "gpt-5.4-nano", "gpt-5.5"] as const)(
+		"sends none reasoning effort for OpenAI %s when no reasoning is requested",
+		async (modelId) => {
+			const model = getModel("openai", modelId);
+			let capturedPayload: unknown;
+
+			vi.spyOn(globalThis, "fetch").mockResolvedValue(
+				new Response("data: [DONE]\n\n", {
+					status: 200,
+					headers: { "content-type": "text/event-stream" },
+				}),
+			);
+
+			const stream = streamOpenAIResponses(
+				model,
+				{
+					systemPrompt: "sys",
+					messages: [{ role: "user", content: "hi", timestamp: Date.now() }],
+				},
+				{
+					apiKey: "test-key",
+					onPayload: (payload) => {
+						capturedPayload = payload;
+					},
+				},
+			);
+
+			for await (const event of stream) {
+				if (event.type === "done" || event.type === "error") break;
+			}
+
+			expect(capturedPayload).toMatchObject({
+				reasoning: { effort: "none" },
+			});
+		},
+	);
+
+	it.each(["gpt-5", "gpt-5-mini", "gpt-5-nano", "gpt-5-pro", "gpt-5.2-pro", "gpt-5.4-pro", "gpt-5.5-pro"] as const)(
+		"omits reasoning effort for OpenAI %s when off is unsupported",
+		async (modelId) => {
+			const model = getModel("openai", modelId);
+			let capturedPayload: unknown;
+
+			vi.spyOn(globalThis, "fetch").mockResolvedValue(
+				new Response("data: [DONE]\n\n", {
+					status: 200,
+					headers: { "content-type": "text/event-stream" },
+				}),
+			);
+
+			const stream = streamOpenAIResponses(
+				model,
+				{
+					systemPrompt: "sys",
+					messages: [{ role: "user", content: "hi", timestamp: Date.now() }],
+				},
+				{
+					apiKey: "test-key",
+					onPayload: (payload) => {
+						capturedPayload = payload;
+					},
+				},
+			);
+
+			for await (const event of stream) {
+				if (event.type === "done" || event.type === "error") break;
+			}
+
+			expect(capturedPayload).not.toMatchObject({
+				reasoning: expect.anything(),
+			});
+		},
+	);
+
 	it("sets cache-affinity headers for official OpenAI Responses requests with a sessionId", async () => {
 		const captured = await captureOpenAIResponseHeaders({ sessionId: "session-123" });