Class HttpxClient

Asks to for a CONNECT tunnel to init.authority (design §4.2). On a 2xx the exit opens one IBB stream and both directions travel on it; the returned tunnel is that stream, with its idle watchdog off — a tunnel is idle by nature, and its liveness is the XMPP session's and the TCP side's business.

Re-derives the sizes the stream's stanza limit bounds — inline request bodies, the chunk size asked of the peer (its stanzas cross our server too) and this client's own IBB blocks — typically from stanzaBudgets(maxBytes) once the server has advertised its limit (XEP-0478; see applyStreamLimits). Requests already in flight keep the sizes they started with.