For the triggers feature, I realized that I could use a CI broker event filter predicate HasFile:

!HasFile .radicle/native.yaml

My use case would be to trigger a CI run with an adapter only if the commit has the relevant file. Something like:

triggers:
- adapter: native
  filters:
  -  !HasFile ".radicle/native.yaml"
- adapter: ambient
  filters:
  - !HasFile ".radicle/ambient.yaml"
``

<https://radicle.zulipchat.com/#narrow/channel/452370-radicle-ci/topic/CI.20broker.20filter.20predicate.20to.20check.20file.20existing/near/495228927>