itest: add test coverage for Taproot tweak key mutation

lntest/itest/lnd_psbt_test.go

@@ -1151,6 +1151,21 @@ func assertPsbtSpend(ctx context.Context, t *harnessTest,
 	finalTx, err := psbt.Extract(signedPacket)
 	require.NoError(t.t, err)
 
+	// Make sure we can also sign a second time. This makes sure any key
+	// tweaking that happened for the signing didn't affect any keys in the
+	// cache.
+	signResp2, err := alice.WalletKitClient.SignPsbt(
+		ctx, &walletrpc.SignPsbtRequest{
+			FundedPsbt: buf.Bytes(),
+		},
+	)
+	require.NoError(t.t, err)
+	signedPacket2, err := psbt.NewFromRawBytes(
+		bytes.NewReader(signResp2.SignedPsbt), false,
+	)
+	require.NoError(t.t, err)
+	verifySigned(signedPacket2)
+
 	buf.Reset()
 	err = finalTx.Serialize(&buf)
 	require.NoError(t.t, err)

lntest/itest/lnd_remote_signer_test.go

@@ -103,7 +103,8 @@ func testRemoteSigner(net *lntest.NetworkHarness, t *harnessTest) {
 			runCPFP(net, tt, wo, carol)
 		},
 	}, {
-		name: "psbt",
+		name:       "psbt",
+		randomSeed: true,
 		fn: func(tt *harnessTest, wo, carol *lntest.HarnessNode) {
 			runPsbtChanFunding(net, tt, carol, wo)
 			runSignPsbtSegWitV0P2WKH(tt, net, wo)
@@ -124,8 +125,9 @@ func testRemoteSigner(net *lntest.NetworkHarness, t *harnessTest) {
 			runSignVerifyMessage(tt, net, wo)
 		},
 	}, {
-		name:      "taproot",
+		name:       "taproot",
-		sendCoins: true,
+		sendCoins:  true,
+		randomSeed: true,
 		fn: func(tt *harnessTest, wo, carol *lntest.HarnessNode) {
 			ctxt, cancel := context.WithTimeout(
 				ctxb, 3*defaultTimeout,