Decisions must carry an expiry

[President]

A decision has no expiry.
The Guardian cannot say "yes, for the next ten minutes".

Without that, a verdict is applied whenever the step finally runs, against state that has moved since.

What I would add:

• expires_at on the decision, optional, ISO 8601
• the Observed Agent checks it before it runs the step
• expiry_disposition on the decision, deny or resubmit, default deny
• on resubmit the step goes to the Guardian again for a fresh verdict
• the Guardian bounds how many times one step may be resubmitted