- TCP single-write fix: combine length prefix + message to avoid split segments that Microsoft/Azure DNS servers reject - Mock server (spawn_tcp_dns_server) updated to use single-write too - Tests: forward_tcp_wire_format, forward_tcp_single_segment_write - Integration: real-server checks for Microsoft/Office/Azure domains Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>