test: reproduce Amino JSON signing bug for MsgSetRoutingIsmDomain

Add a unit test that reproduces the bug where Amino JSON signing fails
for MsgSetRoutingIsmDomain with "unknown protobuf field" because the
nested Route message's field descriptors are not resolvable via
gogoproto.HybridResolver. Also add a TxConfig() accessor to simapp.App
for future integration-level amino signing tests.

Closes #156

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rootulp

tests/simapp/app.go

@@ -251,3 +251,7 @@ func (app *App) RegisterAPIRoutes(apiSvr *api.Server, apiConfig config.APIConfig
 func (app *App) AppCodec() codec.Codec {
 	return app.appCodec
 }
+
+func (app *App) TxConfig() client.TxConfig {
+	return app.txConfig
+}

x/core/01_interchain_security/types/amino_json_test.go

@@ -0,0 +1,91 @@
+package types_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	txv1beta1 "cosmossdk.io/api/cosmos/tx/v1beta1"
+	"cosmossdk.io/x/tx/signing"
+	"cosmossdk.io/x/tx/signing/aminojson"
+
+	"github.com/bcp-innovations/hyperlane-cosmos/util"
+	"github.com/bcp-innovations/hyperlane-cosmos/x/core/01_interchain_security/types"
+
+	gogoproto "github.com/cosmos/gogoproto/proto"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/anypb"
+)
+
+// TestAminoJSONSigningMsgSetRoutingIsmDomain reproduces the bug where Amino
+// JSON signing fails for MsgSetRoutingIsmDomain because the nested Route
+// message's field descriptors are not resolvable via gogoproto.HybridResolver.
+//
+// See: https://github.com/celestiaorg/celestia-app/issues/6541
+func TestAminoJSONSigningMsgSetRoutingIsmDomain(t *testing.T) {
+	// 1. Construct a MsgSetRoutingIsmDomain with a populated Route
+	ismAddr := util.CreateMockHexAddress("routing-ism", 1)
+	routeIsm := util.CreateMockHexAddress("route-ism", 1)
+
+	msg := &types.MsgSetRoutingIsmDomain{
+		IsmId: ismAddr,
+		Route: types.Route{
+			Ism:    routeIsm,
+			Domain: 42,
+		},
+		Owner: "cosmos1testowner",
+	}
+
+	// 2. Marshal with gogo proto
+	msgBytes, err := gogoproto.Marshal(msg)
+	require.NoError(t, err)
+
+	// 3. Wrap as an anypb.Any
+	anyMsg := &anypb.Any{
+		TypeUrl: "/" + gogoproto.MessageName(msg),
+		Value:   msgBytes,
+	}
+
+	// 4. Build a TxBody and marshal to bodyBytes
+	body := &txv1beta1.TxBody{
+		Messages: []*anypb.Any{anyMsg},
+	}
+	bodyBytes, err := proto.Marshal(body)
+	require.NoError(t, err)
+
+	// 5. Build a minimal AuthInfo with a Fee and marshal to authInfoBytes
+	authInfo := &txv1beta1.AuthInfo{
+		Fee: &txv1beta1.Fee{
+			GasLimit: 200000,
+		},
+	}
+	authInfoBytes, err := proto.Marshal(authInfo)
+	require.NoError(t, err)
+
+	// 6. Create an amino JSON sign mode handler with default options
+	// (uses gogoproto.HybridResolver, same as the real app)
+	handler := aminojson.NewSignModeHandler(aminojson.SignModeHandlerOptions{})
+
+	signerData := signing.SignerData{
+		Address:       "cosmos1testowner",
+		ChainID:       "test-chain",
+		AccountNumber: 1,
+		Sequence:      0,
+	}
+
+	txData := signing.TxData{
+		Body:          body,
+		AuthInfo:      authInfo,
+		BodyBytes:     bodyBytes,
+		AuthInfoBytes: authInfoBytes,
+	}
+
+	// 7. Call GetSignBytes — this is where the bug manifests.
+	// The handler internally calls RejectUnknownFields which descends into the
+	// nested Route message and fails because its field descriptors are not
+	// properly registered in the google.golang.org/protobuf registry.
+	signBytes, err := handler.GetSignBytes(context.Background(), signerData, txData)
+	require.NoError(t, err, "GetSignBytes should succeed for MsgSetRoutingIsmDomain")
+	require.NotEmpty(t, signBytes)
+}