IMO "coverage" does not need to be enabled at all. For FEATURES=test "unittests" is enough. And with "zstd" set the "zstd-advanced-apis" should be enabled. I do run a modified ebuild [1] at 2 relays and 1 client with that modification w/o any issues so far. [1] https://github.com/toralf/tgro/blob/master/net-vpn/tor/tor-0.4.3.5.ebuild