compact-core:compact-transaction-model

Midnight transaction execution maps Compact circuits through three stages: well-formedness, guaranteed, and fallible phases. The kernel.checkpoint() function defines boundaries between these phases, ensuring proper state validation and ZK proof verification before on-chain commitment.

Use kernel.checkpoint() in Compact contracts to separate the guaranteed phase from the fallible phase. This separation is critical when handling transaction composition, atomic swaps, and state-conflict scenarios where consistent phase boundaries must be maintained for ZK proof verification.

Transaction composition in Midnight merges multiple Compact circuits within the fallible phase to execute atomic swaps. The Zswap transcript binding ensures consistency across merged transactions, while gas-to-fee calculations determine the execution costs for the composed transaction.

The guaranteed phase executes operations that must succeed without consuming fees, while the fallible phase handles operations that may fail and incur gas costs. Kernel.checkpoint() defines this boundary, allowing developers to implement fee-aware contracts with proper state-conflict handling.

Gas-to-fee calculations in Midnight contract deployments occur during the fallible phase after kernel.checkpoint() separates it from the guaranteed phase. ZK proof verification and transcript binding ensure that fee accounting remains consistent across the deployed Compact circuits.

ZK proof verifications are required in Midnight transaction semantics to validate that Compact circuits execute correctly across well-formedness, guaranteed, and fallible phases. They ensure state consistency during transaction composition and contract deployments while maintaining robust fee-aware guarantees.