The `::1` companion listener added in #8081 cannot bind on hosts with
IPv6 disabled at the kernel (ipv6.disable=1). Bun reports that failure
with its generic "Is port X in use?" message (oven-sh/bun#7187), which
isAddressInUse misread as a real collision, tearing down the healthy
IPv4 listener and throwing a bogus "port 1455 is in use"
ConfigurationError that blocked Codex login.
#createServer now probes os.networkInterfaces() for an internal IPv6
loopback up front and serves IPv4 alone when none exists, instead of
relying on Bun error classification the message ambiguity defeats.
Fixes#8814
roboomp
8ae547091f