lighttpd ssl.* directives can be inherited from the global scope (without needing to be repeated in each condition) if the only ssl.* directive in a socket condition is $SERVER["socket"] == "..." { ssl.engine = "enable" }
conf-available/10-ssl.conf and use-ipv6.pl can be modifed to achieve the behavior requested in this bug. Proposed patch: https://salsa.debian.org/debian/lighttpd/-/commit/3487cb5dbf39a588af2134822c64fdcae197a523