For offramping Asset Hub USDC, we need to implement a new flow structure that starts with the Asset Hub.

Different flow structures will also imply that other parts of the code are more generic, e.g., the OfframpingState type.

Proposal

• for simplicity, we can just reuse the current definition of OfframpingState for the new flow
  • squidRouterApproveHash, squidRouterSwapHash, moonbeamXcmTransactionHash will not be required but they are defined as optional anyway
  • squidRouterReceiverId and squidRouterReceiverHash are determined in constructInitialState
    but we can keep this logic as we can use it to show a unique id to the user (Update transaction ID shown to the user #193)
• add a new field to OfframpingState that describes the type of flow (e.g., "type": "evmMoonbeam" | "assetHub")
• add a new phase assetHubXcm and a handler
  • the handler will create an XCM transfer transaction the way it is defined [in this comment] (https://github.com/pendulum-chain/tasks/issues/427#issuecomment-2472873799) – i.e., leave WeightLimit: Unlimited
  • the handler will then use the Polkadot wallet integration to sign and submit this transaction
  • the handler will finally switch to the phase subsidizePreSwap
• remove the initial wait for the squidRouterSwapHash evm transaction from the pendulumFundEphemeral phase handler
• in prepareTransactions phase handler proceed to
  • phase squidRouter if state.type === "evmMoonbeam"
  • phase pendulumFundEphemeral if state.type === "assetHub"
• in pendulumFundEphemeral phase handler proceed to
  • phase executeXCM if state.type === "evmMoonbeam"
  • phase assetHubXcm if state.type === "assetHub"

Note

The new flow structure is not explicitly defined in the file src/services/offrampingFlow.ts but implicitly defined by the successor phase returned in every phase handler.

Whereas the initial structure of the evm-moonbeam flow is:

• prepareTransactions
• squidRouter
• pendulumFundEphemeral
• executeXCM
• subsidizePreSwap

the structure for the Asset Hub flow is:

• prepareTransactions
• pendulumFundEphemeral
• assetHubXcm
• subsidizePreSwap