Message tracing
===============

Happy path::

   1. Load signed config (reject if unsigned).
   2. seal(body) -> envelope with to + ct + lookup_id.
   3. Publish verae.sm.send.
   4. Leaf acks {accepted:true, lookup_id}.
   5. Recipient opens ct with NPE (prod) or lab-xor (lab).

Failure path::

   1. Leaf cannot deliver.
   2. Build Network Error Bundle (no mail body).
   3. Publish verae.sm.dead and verae.sm.error.
   4. Sender opens ct_sender; ops opens ct_system.
   5. Summary to verae.sm.log.summary.