feat(ai): add Mistral Medium 3.5 model (#4009)

packages/ai/test/mistral-reasoning-mode.test.ts

@@ -63,4 +63,18 @@ describe("Mistral reasoning mode selection", () => {
 		expect(payload.promptMode).toBe("reasoning");
 		expect(payload.reasoningEffort).toBeUndefined();
 	});
+
+	it("uses reasoning_effort for Mistral Medium 3.5", async () => {
+		const payload = await capturePayload(getModel("mistral", "mistral-medium-3.5"), { reasoning: "medium" });
+
+		expect(payload.reasoningEffort).toBe("high");
+		expect(payload.promptMode).toBeUndefined();
+	});
+
+	it("omits reasoning controls for Mistral Medium 3.5 when thinking is off", async () => {
+		const payload = await capturePayload(getModel("mistral", "mistral-medium-3.5"));
+
+		expect(payload.reasoningEffort).toBeUndefined();
+		expect(payload.promptMode).toBeUndefined();
+	});
 });