Ethereum Layer-2 (L2) ecosystems improve scalability but also fragment users, liquidity, gas funding, and execution across rollups. Consequently, cross-rollup interoperability is not only a bridging problem but also a wallet, execution, and validation problem. Ethereum Interop Layer (EIL) proposes a voucher-based architecture in which users create voucher requests on an origin chain and redeem XLP-signed vouchers on a destination chain. When reproducing the evaluated SDK version in a controlled local environment, we observed a compatibility issue in the \texttt{UserOperation} path: paymaster-related data can differ after signing, preventing a stable comparison between the user-authorized representation and the representation later inspected by the local validation flow. This paper presents a reproducible two-L2 validation framework and a controlled compatibility mitigation for that issue. We build a deterministic local testbed over Arbitrum- and Optimism-style development chains, deploy the core paymaster and bridge-related components, implement mock bundlers and event-driven XLP providers, and introduce a sanitized paymaster-data handling path together with a compatible multichain account wrapper. Using this framework, we execute the core voucher lifecycle from request creation to destination-chain voucher redemption and asset release. The contribution is an empirical diagnosis of an implementation-level compatibility barrier, a bounded mitigation that restores controlled end-to-end execution, and an inspectable validation artifact for studying voucher-based interoperability. The work does not claim a new interoperability protocol, universal wallet compatibility, or production readiness; it identifies the remaining gaps toward standard-account validation, one-signature multichain authorization, and full dispute-settlement support.

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