Directly Cached Files aren't being generated

When a directory is added to the directly cached files section of the settings page it doesn't create the cached index.html.

The directory is created but not the index.html and there's no mention of it in the debug log.

Fix creating the index.html and add debug log entries if required.

Start at the settings page's directly cached files section and reproduce adding a directory. Trace the cache-generation path for that directory and check the debug log behavior. Done means the directory receives a cached index.html and relevant debug entries are present when generation is attempted.

Written by the indexing model from the issue text.