asset-engine's seed_surface contract needs reproducibility.seed_field to name
which CatalogField carries the seed so the UI can render a Roll button and the
server can fill empty seeds before persistence. SAO's seed field is type=number,
satisfying CatalogService._validate_seed_field.
ace-step is intentionally not declared here — actual_seeds is type=json (a list)
with an upstream reproducibility gap; the planned fix surfaces resolved seeds via
response header, pending a separate contract.
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