The Symfony Filesystem component is a standalone PHP library (published on Packagist as symfony/filesystem) providing two primary utilities: the Filesystem class for filesystem operations — copy, mkdir, touch, remove, chmod/chown/chgrp, rename, symlink/hardlink, readlink, directory mirroring, tempnam, atomic dumpFile, appendToFile, and readFile — and the Path class for cross-platform path string manipulation: canonicalize, normalize, join, makeAbsolute/makeRelative, getLongestCommonBasePath, isBasePath, root/directory/extension extraction, and home-directory expansion. It targets PHP >= 8.4 and depends only on Symfony's deprecation-contracts plus ctype/mbstring polyfills, so it runs in any PHP project without framework baggage, with a small focused exception hierarchy (IOException, FileNotFoundException, InvalidArgumentException, RuntimeException). The craftsmanship lives in the details. dumpFile() writes via a private temporary file and an atomic rename, preserving existing file permissions and following symlinks to their real target; tempnam() uses fopen mode 'x+' to atomically check-and-create (eliminating TOCTOU races), forces umask(0o077) for secure default permissions, retries on collision, and supports stream wrappers like gs:// and file://. All native filesystem calls are routed through a box() wrapper that converts PHP warnings into structured IOException exceptions carrying the offending path. Path.php handles genuinely hard cases — Windows drive letters and the 'C:' special case, phar:// and other stream schemes, dot-segment collapse that preserves leading '..' on relative paths, and dotfile names when the base path is root — with a bounded memoization buffer to keep canonicalization fast. The architecture is deliberately minimal: no container, no services, no event system — just two well-factored classes backed by an exhaustive test suite. PathTest alone contains hundreds of data-provider cases covering UNIX, Windows, and stream-wrapper variants of every operation, and FilesystemTest exercises real filesystem behavior including permission edge cases, symlink privilege failures, read-only directories, and PHP bug workarounds. The component is the 8.2 development branch of Symfony, actively maintained with current dependency requirements and zero notable technical drift.