The manifest.json files marks files that are meant to be used directly with entry: true. Files without this marker are called "chunks", they just exist to house code that is reused between different entry point files, and their existence is not stable (if the import relationships in the code change, those files could be renamed or deleted in a future release without warning).
For this reason, CodexModule should throw an error if something is listed in codexComponents that does not correspond to an entry point file.
(This will require fixing T353190 first: right now too many things that we'd like to be able to use in codexComponents are not yet designated as entry points.)