Currently, if a swaps transaction fails, we show the same error screen whether the failure happened only within metamask (before the transaction was published) or on-chain. These deserve distinct error messages and information. In the case of failures that happen before publishing, no gas was used and no etherscan link will be available.

After #9947, a further distinction in off-chain failures can be drawn: between those that fail due to the estimateGas call failing at the time of creating the swap tx, and those that fail for any other reason.