Cache the current scroll position and URL on the server
Republish the current scroll position and URL during handshake

This makes the controlling browser proactively freshen the server state,
instead of allowing the server to send stale state to mirroring browsers
until a user interaction causes the controlling browser to send a message.
Send the current scroll position and URL in subscription messages
Restore state when subscription messages are received
Insert Apple-specific <meta> tag into each page

This allows the proxied site to run as a full-screen web app on iOS.