- Move regex compilation to package level (was recompiled per call)
- Fetch takeover fingerprints once instead of per-domain HTTP request
- Fix defer resp.Body.Close() leak inside loop (extract fetchDomainBody)
- Store SPF text in ParsedIncludeRecord to avoid re-fetching in debug
- Extract preferIPv4() and mechanismCount() to deduplicate repeated patterns
- Remove dead allocation in parseSPFRecord
- Replace writeToFile wrapper with os.WriteFile
- Remove dead output file logic in processDomainFile
- Clean up ~25 stale/unnecessary comments
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>