List complex predictions for one variant, newest-first.
?variant_id= is required. The listed envelopes carry status +
credit_cost + inputs but not the typed results object;
fetch the single resource with
GET /v1/complex-predictions/{id} for full output including the
signed PDB URL.
Cost: read — rate bucket only.
Bearer authentication header of the form Bearer <token>, where <token> is your auth token.
1 <= x <= 200