When a client deselects an IPv4 exit node, the auto-generated IPv6 default
route (::/0) was still selected and pushed onto the tunnel interface, even
though the user disabled the exit node. On an exit node without a real IPv6
egress this blackholes IPv6 traffic, and because clients prefer IPv6 (happy
eyeballs) it can break general connectivity.
Root cause: the synthesized v6 route gets a different NetID than its v4 base
(base + "-v6"). The route selector keys deselects by NetID and defaults
unknown NetIDs to selected, so the "-v6" entry was never matched by the v4
deselect. The effectiveNetID() mirror that solves exactly this is used by
HasUserSelectionForRoute and FilterSelectedExitNodes, but categorizeUserSelection
called the raw IsSelected(), bypassing it and mis-categorizing the v6 pair as
user-selected.
Add RouteSelector.IsSelectedForExitNode(), which applies effectiveNetID before
the selection check, and use it in categorizeUserSelection. IsSelected() is left
untouched so non-exit code paths don't make unrelated "*-v6" routes inherit v4
state. Adds regression tests for the v4/v6 deselect mirror and explicit-v6
override.
c7499cf8fc