Whatever happened to IPv6 site-local and link local address ranges (address ranges that were specifically defined as address ranges that would not cross router or WAN boundaries? They were in the original IPv6 standards, but don't seem to be implemented or supported. Or at least they aren't implemented or supported by my completely uconfigurable home cable router povided by my ISP.
IPv6 in normal ethernet/wlan like uses requires link-local to for functioning neighbour discovery (equivalent for v4's ARP) so it's very likely it works. Not meant for normal application usage though. Site local was phased out in favour of ULA etc.
But if you're not using global addresses you're probably doing it wrong. Global addressing doesn't mean you're globally reachable, confusing addressing vs reachability is the source of a lot of misunderstandings. You can think of it as "everyone gets their own piece of unique address space, not routed unless you want it to be".