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b8f139c91f
On iOS the route notifier delivered each prefix update from its own fire-and-forget goroutine (notify -> `go func`), so Go provided no ordering guarantee between consecutive updates. It also read currentPrefixes inside that goroutine without holding the lock, racing the next OnNewPrefixes write. On exit-node disable the core removes the default routes as two separate prefix updates (0.0.0.0/0, then the synthesized ::/0). When the two goroutines were reordered, the stale snapshot still containing ::/0 was delivered last and clobbered the correct default-free one. iOS then kept the ::/0 default route on the tunnel with no exit node to carry it, black-holing all IPv6 traffic while IPv4 recovered correctly. Fix: deliver updates through a single worker goroutine fed by a buffered channel, preserving production order, and snapshot the joined prefix string under the mutex so it can't race a concurrent update. Buffered so producers (which run under the route manager lock) don't block on the listener callback.