## Why
The default resolver misses macOS supplemental resolvers and VPN split DNS, preventing Codex from reaching hosts that depend on those DNS settings.
## What changed
Use `tokio::net::lookup_host` for IPv4 and IPv6 lookups in the macOS TCP connector, including connections to upstream proxies. Preserve existing checks on resolved destination addresses and reject unsupported TXT lookups without falling back to a different resolver.
## Testing
Add macOS tests for IPv4 and IPv6 localhost resolution and connections, local-network rejection, and resolving the upstream proxy instead of the destination.
GitOrigin-RevId: 3c7fc4f8b309e26b02923d8fafd4e1f1e1f7755f
