The lexer tokenizes Lux source code written entirely in Lux itself. Supports all token types: keywords, operators, literals, behavioral properties, doc comments, and delimiters. This is the first component of the Lux-in-Lux compiler, demonstrating that Lux's pattern matching, recursion, and string handling are sufficient for compiler construction. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>