Workflows fail with 'Copilot is not a user' error on agent-created PRs #18556
Description
When GitHub Copilot agents create PRs, the actor is set to 'Copilot', causing the activation job's compute_text.cjs to fail when checking collaborator permissions.
Error: RequestError [HttpError]: Copilot is not a user
URL: https://api.github.com/repos/{owner}/{repo}/collaborators/Copilot/permission
The compute_text.cjs action should gracefully handle non-user actors (bots, apps) instead of attempting to check collaborator permissions.
Version: gh-aw v0.50.5
Actor: Copilot (from GitHub Copilot agent-created PRs)