Arcana is a general-purpose sidecar architecture for applications that require fast, deterministic state execution alongside on-chain security guarantees. It operates next to a main chain, currently EVM, and divides system responsibilities along clean architectural lines. The on-chain layer handles custody, deposits, withdrawals, and optional state checkpoints, all enforced through Solidity contracts including UserVault and BackupRegistry. The off-chain layer runs application logic as WASM state machines, typically authored in AssemblyScript with optional Zig support, executing inside the Arcana node as deterministic pure functions with structured input and structured output. The bridge between these layers is the Arcana node itself, written in Rust, which orchestrates execution, persists state through AEDB, watches on-chain events, and applies capability effects such as bank transfers and billing charges atomically with each state transition.