While reviewing #1372, it became clear that the best way to handle test-only BPO forks is to generate them on the fly during the CI fixture building process using the new_fork tool.

This approach avoids:

• The need to modify the t8n interface to support new_fork before running tests, which would otherwise complicate the workflow. Instead, the process can be integrated after welding because everything is in the same repo and branch.
• Having to commit these test-only forks into any branch, or having to rebase these BPO forks if anything changes in the base fork.

Proposed workflow:

1. Define a bpo_test_forks.yaml file containing the parameters for each BPO fork.

• This file is parsed only during CI fixture building.

2. Before running fill (still in the CI environment), invoke the new_fork tool once per BPO fork to generate each required EELS BPO fork folder.
3. Run fill to generate the BPO tests.

Outcome:

• These BPO test-only forks are generated ephemerally and never need to be committed to any EELS branch.
• The solution keeps BPO forks isolated to the testing process, reducing maintenance overhead.