Why would you put that uncensored comment out here for us to see? Now I'm going to have nightmares as if directed by John Capenter about spiders that look exactly like puppies to humans until they attack.

Ohhhh, that's a really cool & outstanding thought!
(With a satisfying explanation for the biological size limits ofc. It can just be "magic", idk, the idea is too nice to be cockblocked by a plot hole.)

It would be even funnier if the arachnids lost some original traits in favour of mimicry & their new environments (like the jumping spoders in this post lost the jumping part for their ant masquerade).

Not the jumping, but like the way of life - they just figured dogs have it too good when bonded to nice humans so some jumping-dog spiders just decide they want to be pets so they cuddle & fetch their entire lives (sure the humans might fund it suspect how many live snacks they have to feed their pupper, or how no smol animals seem to hang around the house, but that's not that different to having a cat).

Also nothing beats the feeling of a happy jumping-dog spider jump-hugging you when you get home with all its weight.

Also jumping-dog spiders - kinds of puppy eyes!

The mammal head tilt still needs some (evolutionary) work tho: