How do web browsers handle cancelled requests? Subjectively speaking, it feels like browsers can take a while to recover from cancelling the loading of a large page/page with a large number of assets. Could this be part of that?

you're right. Cancel's in H1 are very painful because all the in-progress transactions have to be torn down completely. New transactions have to set them all up again.

H2 let's you just send the server a short message that says "stop sending that stream" and you can go ahead and pipeline a new request right along with that cancel.

This happens a lot more than you think as you browse through a collection of things and are just scanning them and clicking the next button - that's a really common use case h2 will handle much better.

Ah, sorry, I misread your question! I don't actually know the lengthy reasoning for that edge case. =(

No problem, I see I was not clear. Yes, I am specifically curious about the edge case when you "can't" just disconnect the TCP. Scare quoted because I'm sure you can, it just involves something undesirable happening. I have vague ideas and guesses, but I'm curious about what the intent was.