`JEV_TRACE` alone cannot be joined to a decision: it records a time to the
second and the answers, with no run, step or action, so nothing in it can be
traced back to a run.
Wrap the client in `RecordingClient` so the last call's questions and answers
travel with the decision row they produced, and give each process a
`SESSION_ID` so rows from two sessions in the same second stay apart. Diff the
history directory before and after a session to attribute the run records it
produced.
What this supports is arm-level analysis: this decision belongs to this session,
and the session's outcome is the run file. It does NOT say whether an individual
answer was correct -- one run result attached to one step cannot label that
step. Per-decision accuracy needs replay, expert judgement, or ground truth the
code can verify on its own (lethal, legality, affordability).
A decision that asked nothing must carry no answers, so `client.last` is
cleared before each decide(); otherwise rows silently inherit the previous
step's answers.
