Structural Admissibility in Blockchain Transactions: The Onion Field Model and its Application to L2 Pre-Submission Governance

This paper presents the Onion Field Model (OFM), a deterministic, non-inferential framework for evaluating the structural admissibility of blockchain transactions before submission to a network. It describes the framework architecture, the invariant schema applied to Layer 2 smart contract interactions, the methodology used to build a live transaction corpus from Base and Arbitrum mainnets, and the findings that corpus produced. 202 live transactions were evaluated on 22 March 2026. 73% were structurally admissible. 26% were rejected, every rejection being an ERC-20 approve() call failing to explicitly state the asset being approved — a structural property of the ERC-20 standard identified consistently and without inference. Engine version OFM-0.1.0. Patent pending: GB2606072.3.