Tectonic is a modernized, self-contained TeX/LaTeX engine that compiles .tex documents to PDF or HTML. It is built on a fork of XeTeX and integrates BibTeX, font shaping via HarfBuzz/FreeType, SVG-to-HTML conversion, and full PDF output via xdvipdfmx. The architecture is a Rust workspace with multiple crates implementing engines, I/O abstraction, bundle management, and C library bridges. The CLI tool provides subcommands (build, watch, new, bundle, dump, show) and supports workspace configuration via Tectonic.toml. The system is production-ready, with extensive test coverage, fuzzing, and support for cross-compilation. While the core TeX engine remains in C/C++ with global state, the Rust layers provide clean abstractions (IoProvider, StatusBackend, CachableBundle) that are reusable and well-architected. The codebase is actively maintained, with regular commits and CI/CD pipelines, though some C components show age and legacy patterns.