Generally looks good to me, but I'm sufficiently shallow on QUICK-related stuff that I might miss something QUIC-incompatible.

Nit: Section 1: The link to "Appendix A.3" is wrong, seems to just link back to this draft.

Issue: Section 2, 2nd paragraph: It feels like there could be a MUST or SHOULD in here so Websockets implementers can be sure they're doing the right thing to get an orderly shutdown?

Issue: Section 2, 4th paragraph: This makes perfect sense, but is it Websockets-specific?  Does it actually belong in  draft-ietf-quic-http?