Directory to group content files without influence on without creating influence on url sections etc

What is the simplest way to use folders to group content files without changing the url or section tree ? Like a leaf bundle, but simpler, hugo would just flatten the directory. I won’t use leaf bundle because I need my files to bear their name, “index” is a no-go.
What I mean:

.
├── archives
│ ├── au-delà-de-l-œdipe.css
│ ├── au-delà-de-l-œdipe.en.html
│ └── au-delà-de-l-œdipe.html
├── auteur.en.md
├── auteur.md
├── essai
│ └── a.md
├── _index.en.md
└── _index.md

it should read three as if the content was of “essai” was raised one level.

If I got it right you can configure a combination of cascade and permalinks in your hugo.toml to achieve that:

  • do not render the section page for /essai/
  • render all pages below /essai/ to the Root
    /essai/a.md is rendered to /a/index.html and linked as /a/ (unless you have uglyUrls set to true)
# suppress render of  the grouping folder"
[[cascade]]
   [cascade.build]
      render = "never"
   [cascade.target]
      path = "{/essai}"

# redirect the urls for grouping folder content
[[permalinks]]
   pattern = '/:slugorcontentbasename'
   [permalinks.target]
      path = '{/essai/**}'

you can tweak the filename, targets, … see:

hint: use --printPathWarnings to check for duplicates

Thought of that… but I was looking for a simpler way.