refs registry

Derived catalog of heading slugs from compile output, typically written as refs.json under outputDir. It lists the headings of each file compile writes, slugged file by file. Those files are every compiled guide and the monolith, and a compiled guide can be a publish output. Parent concept: refs.

The registry is generated state, not authored shards. merlon compile, merlon refs-gen and merlon check rewrite it from their own compile. merlon refs-check compiles without writing and fails when the file on disk no longer matches, as Stale registry check says. Refs registry path gives the path rules, and registry contents lists its fields.