Same Bytes, Different Scene: A Semantic Contract for Portable 3D Gaussian Splatting

Learned three-dimensional representations increasingly leave the system that trained them and are consumed by heterogeneous converters, importers, and renderers. For Gaussian splatting, serialized parameters do not alone determine a scene because consumer code completes their meaning along two coupled dimensions: bounded admission, covering schema, extent, and resource commitments, and semantic portability, covering rotation, coordinates, and radiance. The same accepted asset can therefore denote different scenes across consumers: a semantic polyglot. We formalize this problem with a typed cross-implementation observation model and root-adjudicated differential semantics, which promotes a disagreement only after invariant reduction, source localization, and stable replay. SplatContract then enforces a format-explicit boundary: it proves bounded structure before size-proportional allocation, constructs a canonical Bounded Gaussian Intermediate Representation (BGIR), and removes source-byte authority at handoff. Across five formats and six implementation families, adjudication isolates four causal mechanisms spanning both dimensions. SplatContract blocks all four while admitting 99.975% of 8,000 sealed legal assets, and it recovers matched scene interpretations on calibrated real scenes.