Retrofit of https://github.com/ccheever/llp. Ten LLP docs capture the
design rationale (trust model, engine pipeline, runtimes, config,
verification, sources/reporters, CLI, templates); 161 @ref comments link
code to the sections that explain it. ref-check (copied from upstream,
dependency-free) validates refs and metadata on every push and PR.
Every rationale claim is tagged [observed] with its evidence.
