[
  {"op": "doc", "text": "attempt to enter an arg-bearing type half-configured: Session with no construction args"},
  {"op": "source", "role": "price", "kind": "F64"},
  {"op": "add", "type": "Session", "name": "sess", "bind": {"period_minutes": {"I64": 15}}},
  {"op": "feed", "role": "price", "into": ["sess.trigger"]},
  {"op": "expose", "from": "sess.bars_since_open", "as": "bars"}
]