A truly excellent essay.

I would venture to say that the distinction between moral clarity and moral certitude is the biggest obstacle to a morally based foreign policy.

Moral certitude is a goal that can never be ultimately reached; although the attempt leads to greater and greater moral clarity. Unfortunately, moral certitude is where many people believe they start. Certitude is the mind's life raft in a sea of divergent opinion, and even when that raft is made of stone, the mind is loathe to give it up.
Because this is a foible of the human condition, your external tests for moral clarity in foreign policy must also become recursive. Is another nation's advice derived from certitude? Is the group think of your advisors reflective of certitude? Any test proposed will only be effective if that tests have passed its own testing process.

I hope this demonstrates some understanding of your thoughts. As with all philosophies and most all scientific theories, it is the 'a priori' with which one begins that drives the body of the work.

Thanks for an intriguing read.