macOS 26 silently breaks custom DNS resolution for developers using `/etc/resolver/` files. The update causes `mDNSResponder` to intercept queries for non-IANA TLDs like `.internal`, `.test`, and `.home.arpa`, treating them as multicast DNS instead of consulting the configured unicast nameserver. This breaks workflows that have worked reliably since macOS 10.6.

Developers using dnsmasq, Docker Desktop, and similar tools for local development are affected. The failure is particularly problematic because `scutil --dns` shows resolver configuration as registered, creating a false sense of correctness while resolution silently fails. RFC 6761 explicitly reserves `.test` for local testing, yet macOS 26 overrides this standard behavior.

The only workaround is manual `/etc/hosts` entries, which is impractical for dynamic environments like container orchestration. This impacts Kubernetes development tools, VPN clients, and any software that generates resolver files automatically. The regression affects Apple Silicon machines running build 25D771280a and represents a significant disruption to established macOS development practices.