Local composite actions always relative to top level repository

Describe the bug

I'm building a set of actions for my organization, and I would like to re-use common sections as composite actions. This appears to be the motivating case around https://github.com/actions/runner/issues/646, and it certainly suits my needs.

However: I have a pattern like:

main repo

- uses: actions/checkout@v2-beta # check out your code
- uses: actions/checkout@v2-beta # check out the actions repo
  with:
    repository: my-org/github-actions
    ref: refs/tags/v1
    path: github-actions
- name: Run the private action
  uses: ./github-actions/build-em-all

then in my-org/github-actions /build-em-all/action.yml

#...
- uses: ./do-tedious-setup

My dilemma here is that the above won't work - the action is looked up relative the the consumer's workspace; so it should be - uses: ./github-actions/do-tedious-setup - but that's entirely dependent on the checkout in the consumer! The actions library has to expect that it's checked out in the right directory, which itself imposes a restriction on the file structure of consuming projects.

Even if I were to parameterize the checkout location, the uses field (probably rightfully) doesn't get any contexts to work from, so I can't deliver the input.

For the moment, I'm settling on documenting the requirement and hoping it doesn't cause a problem.

Expected behavior

It'd be great if actions were looked up with a Bash style PATH behavior and that a workflow could append items to the lookup list.

Runner Version and Platform

Version of your runner? Github hosted ubuntu-latest

Start by tracing how the workflow's uses field resolves local composite actions, then compare that behavior with the nested action.yml example in build-em-all. Determine how resolution could use the checked-out action library rather than the consumer workspace, and define completion as nested actions working without requiring a fixed checkout directory.