Add integration test for MuSig2RegisterCombinedNonce and
MuSig2GetCombinedNonce RPCs to verify the coordinator pattern workflow.
The test:
- Creates three signing sessions without initial nonce exchange
- Manually aggregates nonces using the coordinator pattern (btcec musig2)
- Tests v0.4.0 returns unsupported errors (as expected)
- Tests v1.0.0rc2 successfully registers and retrieves combined nonces
- Verifies mutual exclusivity (error: already have all nonces)
- Completes a full signing flow to ensure signatures are valid
Also adds the required RPC harness wrapper methods to lntest/rpc/signer.go for
the new RPCs and adds MuSig2RegisterNoncesErr wrapper for error testing.
Elle Mouton
fb48697ffa