Dentists run a business
While there is no requirement to warrantee or guarantee anything, basic business principles matter. If a dentist makes bad business decisions, they won't be in business for very long. If your request is reasonable, perhaps.
If the crown is BONDED and not cemented, the crack may not matter. Natural teeth have cracks, called crazed lines, that don't matter much. The crack may not get any worse, depending on the material and luting process.
Porcelain crowns can fracture for any number of reasons from you grinding your teeth to biting on something that is too hard. I suggest you talk to your dentist to see what the policy is for recently done crowns that fracture. There is no nation wide guarantee. It is up to the dentist to set their own standard. Good luck!
It is possible that a porcelain crown was made with an inherent crack that was not noticeable when cemented. However, usually when a crown or tooth breaks, there is some bruxism going on while sleeping. Most people are not even aware that they do this. A perceptive dentist would be able to detect signs of clenching or grinding at night. As far as a guarantee goes, I tell my patients that if anything goes wrong that is not due to lack of proper hygiene, then I guarantee my work for 1 year. It will last much longer than this of course. Bruxism will cause most dentistry to fail eventually and should be diagnosed early.