Magic Routing Hint

[rajarshimaitra]

This code adds the Magic Routing Hint logic. As most of the logic is at the application layer, the code is added in the test cases of v2 swaps.

No changes in the internals of the library is required.

This is untested. And to test it one has to perform the following.

• Initiate a reverse swap with Boltz.
• Use the invoice received in reverse swap and initiate a submarine swap with the same invoice.

[i5hi]

Thanks @rajarshimaitra !