A decoded inbound webhook body: a JSON object OR a JSON array.

Vendors differ in wire shape — ComplyCube delivers top-level objects, HubSpot batches top-level ARRAYS of event objects — and the ledger of record persists what the vendor signed, not a normalized remix of it. Storage is identical to :map (jsonb / JSON text) and every value Ash.Type.Map accepts still casts: this is a strict superset whose only addition is the list shape. A JSON string body (the raw undecoded wire) is accepted and decoded, mirroring :map's convenience cast.