Does the MacBook Air's warranty cover screen issues?

Possibly. Apple keeps changing the rules on what is considered accidental damage. Years ago, this would be considered accidental damage. Just a few years ago it may have been covered if there were no other signs of accidental damage & it was just a single crack. Today, I'm not so sure if a single hairline crack is covered.

You need to have Apple or an Apple Authorized Service Provider examine the laptop to make the final determination. Apple always has the final say on all warranty coverage matters.

As you can see, you can only get an official answer to this from Apple, but they do not respond in this user-to-user forum setting.

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I'm with Tim: was anyone else near the device? It almost looks like that corner got torqued. How about a pet? In my early days with Mac laptops, cats had a tendency to sleep on warm laptop keyboards. That's when I gained the habit of closing my Macbook Pros' lids when I stepped away. I won't mention the number of posts here where someone's kitty left a bio-sample on —and in—the keyboard 😳

Unlikely that damage would be covered by the warranty. You should have it inspected for your options.

Probably not. That's physical damage to the LCD. Might want to hunt down whoever might have had access to it while you were in the can...