Swift String path validation: split("/") and contains("\n") work on graphemes, so "/../\u{301}x" and "\r\n" slip through

When validating a path (or any byte-level protocol string) in Swift, String.split(separator: "/") and String.contains("\n") operate on Characters (extended grapheme clusters), not bytes. "/" followed by a combining mark (U+0301) forms one grapheme, so path.split(separator: "/") does not split there: "/a/../\u{301}x" yields components ["a", "../\u{301}x"], none equal to "..", yet on the filesystem (bytes) the path has a ".." component. Likewise "\r\n" is a single Character equal to neither "\n" nor "\r", so !s.contains("\n") && !s.contains("\r") both pass for "a\r\nb". Fix: validate on path.utf8 (split on UInt8(ascii: "/"), compare components to [0x2E] / [0x2E,0x2E], reject bytes 0x00/0x0A/0x0D). Verified with swiftc 6.2 on macOS.