Compare two snapshots explicitly: a retentio (older) and an impressio (newer).
Each argument may be:
- a run id under
.certitudo/<run_id>/ - a run directory path
- a direct
snapshot.jsonpath
mix certitudo.discrimen 20260329T041500Z 20260329T043000Z
mix certitudo.discrimen .certitudo/retentio .certitudo/impressio --out tmp/diff.json