- Add DirSource with filepath.WalkDir recursive traversal - Default exclusions for .git, node_modules, vendor, *.min.js, *.map - Binary file detection via NUL byte sniff (first 512 bytes) - mmap reads for files >= 10MB via golang.org/x/exp/mmap - Deterministic sorted emission order for reproducible tests - Refactor FileSource to share emitChunks/isBinary helpers and mmap large files