tapchannel: update registerAndBroadcastSweep for HTLC sweeps

In this commit, we update `registerAndBroadcastSweep` to be able to
handle HTLC sweeps.

First, we only need to set the anchor for first level sweeps.

We weren't able to sign the 2nd level sweeps earlier as we didn't know
the txid of the transaction that swept them. Now that we're about to
broadcast, we know the sweeping transaction so we can set the prevID
properly, then sign the sweeping transaction.

Author: Roasbeef

tapchannel/aux_sweeper.go

@@ -1718,6 +1718,7 @@ func (a *AuxSweeper) resolveContract(
 	default:
 		return lfn.Errf[returnType]("unknown resolution type: %v",
 			req.Type)
+		// TODO(roasbeef): need to do HTLC revocation casesj:w
 	}
 
 	// The input proofs above were made originally using the fake commit tx
@@ -1951,6 +1952,7 @@ func prepVpkts(bRes lfn.Result[blobWithWitnessInfo],
 // none of the inputs have any resolution blobs. Then an empty slice will be
 // returned.
 func extractInputVPackets(inputs []input.Input) lfn.Result[sweepVpkts] {
+
 	type returnType = sweepVpkts
 
 	// Otherwise, we'll extract the set of resolution blobs from the inputs
@@ -2179,7 +2181,8 @@ func (a *AuxSweeper) registerAndBroadcastSweep(req *sweep.BumpRequest,
 		internalKey.PubKey.SerializeCompressed())
 
 	// We'll also use the passed in context to set the anchor key again for
-	// all the vOuts.
+	// all the vOuts, but only for first level vPkts, as second level
+	// packets already commit to the internal key of the vOut.
 	for idx := range vPkts.firstLevelPkts() {
 		for _, vOut := range vPkts.firstLevelPkts()[idx].Outputs {
 			vOut.SetAnchorInternalKey(
@@ -2188,8 +2191,42 @@ func (a *AuxSweeper) registerAndBroadcastSweep(req *sweep.BumpRequest,
 		}
 	}
 
+	// For any second level outputs we're sweeping, we'll need to sign for
+	// it, as now we know the txid of the sweeping transaction.
+	for _, sweepSet := range vPkts.secondLevel {
+		for _, vPkt := range sweepSet.vPkts {
+			for _, vIn := range vPkt.Inputs {
+				vIn.PrevID.OutPoint = sweepSet.btcInput.OutPoint()
+			}
+		}
+	}
+
+	// If we have second level vPkts, then we'll need to sign them here, as
+	// now we know the input we're spending which was set above.
+	for _, sweepSet := range vPkts.secondLevel {
+		tapSigDesc, err := sweepSet.tapSigDesc.UnwrapOrErr(
+			fmt.Errorf("tap sig desc not populated"),
+		)
+		if err != nil {
+			return err
+		}
+
+		err = a.signSweepVpackets(
+			sweepSet.vPkts, *sweepSet.btcInput.SignDesc(),
+			tapSigDesc.TapTweak.Val, tapSigDesc.CtrlBlock.Val,
+			lfn.None[lnwallet.AuxSigDesc](),
+			lfn.None[uint32](),
+		)
+		if err != nil {
+			return fmt.Errorf("unable to sign second level "+
+				"vPkts: %w", err)
+		}
+	}
+
 	// Now that we have our vPkts, we'll re-create the output commitments.
-	outCommitments, err := tapsend.CreateOutputCommitments(vPkts.allPkts())
+	outCommitments, err := tapsend.CreateOutputCommitments(
+		vPkts.allPkts(),
+	)
 	if err != nil {
 		return fmt.Errorf("unable to create output "+
 			"commitments: %w", err)