Snowbridge Unordered Message Delivery - Inbound Queue

[claravanstaden]

Description

Implements the Inbound Queue for Snowbridge v2.

Integration

This PR adds:

• A new pallet called EthereumInboundQueueV2 with a submit extrinsic.
• A new runtime API called InboundQueueApiV2 with a method dry_run, that takes an Ethereum command and converts it to Xcm and provides the execution fee on BH and static fee part of the AH execution.

Since this is a new pallet, no breaking changes are made to the EthereumInboundQueue pallet.

Review Notes

The Inbound Queue v2 pallet expects an abi-encoded envelope from Ethereum. Once decoded, the payload parameter is SCALE decoded into a v2::Message. The message contains:

• origin: The origin address of the user on Ethereum
• assets: A vector of assets that will be placed in the holding on AH. Can be a native ERC-20 or a foreign ERC-20 (Polkadot native assets). The XCM instructions that are used differ per asset type (ReserveAssetDeposited for native ERC-20 tokens and WithdrawAsset for Polkadot native assets). The user on Ethereum specifies additional xcm deposit the asset into a beneficiary account.
• xcm: User provided xcms, to deposit the asset to a beneficiary, provide further fees or other instructions such as Transact (for example, to register a token)
• claimer: The claimer on AH, in case funds are trapped so it can be claimed.

The relayer pays a DOT fee that covers:

• The execution fees on BH
• The static xcm part of the message on AH

The DOT fee is burnt from the relayer account and teleported to AH.

Messages may be processed out of order. Nonces are stored in a sparse bitmap for space-efficient storage.

TODO:

• Westend BH integration tests