Webtransport negotiation with Safari

I am maintaining a node.js package for webtransport build around quiche.
Users are reporting problems with Safari (I do not have a mac, and use only chromium and firefox):
https://github.com/fails-components/webtransport/issues/490#issuecomment-5561999326

I would say, it is caused by missing http3 settings for flow control. (I would guess the proposal with the capsules with zeros, just turn off Safaris flow control, and this is not a good idea).
My guess is that webkit implements a newer draft for webtransport, and I can not do really anything as a user of quiche, and the fix should be done inside quiche. (Are there plans, or do we wait for RFC).
Is my analysis correct?
@vasilvv you know it probably best as you are one of the http/3 wt spec authors and also programmed most of it in quiche.

No file, test, or entry point is named. Start by reading the linked Safari report and the WebTransport negotiation and HTTP/3 flow-control handling in quiche; done requires confirming the compatibility cause and defining a specific, actionable change or documenting that it belongs elsewhere.

Written by the indexing model from the issue text.