Hello, future me. This is for you next time you want to do this.

When setting up the CI for a project I will sometimes end up with a tremendous clutter of workflow runs. Sometimes they have embarrassing mistakes. Who wants to show that to people? I was trying to figure out how to bulk delete workflow runs from the CLI, and I came up with something that works:

gh run list --json databaseId  -q '.[].databaseId' |
  xargs -IID gh api \
    "repos/$(gh repo view --json nameWithOwner -q .nameWithOwner)/actions/runs/ID" \

This will delete all (well, up to 20, or whatever you set in --limit) your workflow runs. You can add flags to gh run list to filter runs by workflow or by triggering user.