Glossary

Aggregation hook / ISM. Combines several hooks (run all) or ISMs (require m of n).

Checkpoint. What a validator signs: a Merkle root, an index and the latest message id, bound to an origin domain and its Merkle tree hook.

Default hook. The hook a Mailbox runs for messages that do not name their own. On Recoil Link: Merkle tree hook plus interchain gas paymaster.

Default ISM. The security module a Mailbox uses for recipients that do not name their own.

Dispatch. Sending a message: Mailbox.dispatch.

Domain id. A uint32 identifying a chain. Equal to the chain id on every EVM network Recoil Link supports.

Hook (post-dispatch hook). Code the origin Mailbox runs after recording a message: Merkle tree, gas payment, protocol fee.

Interchain gas paymaster (IGP). Hook that charges senders for destination gas and pays the relayer.

ISM (interchain security module). Contract on the destination that decides whether a message is genuine.

Mailbox. The one contract per chain apps call to send (dispatch) and that calls recipients (handle).

Merkle tree hook. Records every message id in an incremental Merkle tree that validators sign.

Message id. keccak256 of the packed message; unique.

Metadata. Extra bytes: hook metadata (gas limit, refund address) passed on dispatch; ISM metadata (signatures) supplied by the relayer on delivery.

OIF (Open Intents Framework). Standard contracts for cross-chain intents: escrows, settlers, oracles.

Process. Delivering a message: Mailbox.process(metadata, message), called by the relayer.

Protocol fee. Flat per-message fee charged by the required hook. Zero on Recoil Link today.

RecoilLinkOracle. OIF oracle that proves fills over Recoil Link.

Registry. Public repository of chain metadata and Recoil Link deployment addresses.

Relayer. Off-chain agent that delivers messages and pays destination gas.

Required hook. The hook a Mailbox runs on every message, whatever the sender chooses.

Validator. Off-chain agent that signs checkpoints for one origin chain.

Validator announce. Contract where each validator records, once, where its signatures are stored.