How did Darth Vader know what Luke got him for Christmas?

setup: How did Darth Vader know what Luke got him for Christmas?

[Imperial HR Officer] qua gray uniform, hat, datapad Captain Vader. Welcome to Imperial Holiday Gathering 12-25. Please review the gift exchange protocol.

[Vader] qua black armor, breathing rhythm steady, hand on a wrapped box I do not require briefing.

[Imperial HR Officer] Sir, the protocol is mandatory. The gift exchange is Secret Santa style. You drew Skywalker dash L.

[Vader] Yes.

[Imperial HR Officer] And he drew you.

[Vader] Yes.

[Shakes] qua junior officer with a wrapping-paper cart, beaming This is the best of all possible Sith holidays.

[Imperial HR Officer] Sir. The gift from Skywalker has arrived.

((A SMALL WRAPPED BOX APPEARS ON A DROID-WHEELED CART. BOWS. WRAPPED IN SILVER, EMBOSSED WITH AN X-WING.))

[Imperial HR Officer] Would you like to unwrap?

[Vader] Unnecessary.

[Imperial HR Officer] Sir.

[Vader] ((REACHING OUT WITH A GLOVED HAND, HOVERING)) I sense …

[Imperial HR Officer] Sir, please open the gift.

[Vader] A wool sweater.

[Imperial HR Officer] ((LOOKS AT DATAPAD))

[Vader] Hand-knit. Sky-blue. Slightly itchy. He used the wrong wool.

[Imperial HR Officer] Sir. How do you —

[Vader] ((LIFTS GLOVE)) The Force. Christmas adjacent.

[Manyfeek] qua tag fallen off the gift, lying on the floor ((FROM THE CARPET)) “To Father, from your son. I made this one.” X.O. ANAKIN’S BOY.

[Imperial HR Officer] Sir, you haven’t opened it.

[Vader] I felt it.

[Imperial HR Officer] Through the paper?

[Vader] Through the universe.

[Imperial HR Officer] And the size?

[Vader] Medium. He thinks I’m a medium. I am an extra-large. He never sized me.

[Imperial HR Officer] Will you wear it.

[Vader] ((LONG BEAT)) Yes.

punchline: He felt his presents.