- Send SERVFAIL response (with correct query ID) when resolve_query
fails, preventing DoT clients from hanging until idle timeout
- Extract handle_dot_connection() so tests use the same logic as
production, eliminating duplicated accept/read/resolve loop
- Replace magic 4096 with named MAX_MSG_LEN constant tied to BUF_SIZE
- Add flush() after each TLS write to prevent buffered responses
- Extract fallback_tls() helper, handle partial cert/key config,
support IPv6 bind address, remove redundant crypto provider init
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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