refactor(msg_gateway): restructure and rename message_gateway aligned with custom_example

backend/plugins/domain/msg_gateway/registry_test.go

@@ -0,0 +1,38 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package msg_gateway
+
+import (
+	"context"
+	"testing"
+)
+
+type stubChannel struct{}
+
+func (stubChannel) Type() string { return "stub" }
+func (stubChannel) Connect(context.Context) error {
+	return nil
+}
+func (stubChannel) Disconnect(context.Context) error { return nil }
+func (stubChannel) Send(context.Context, Recipient, OutboundMessage) error {
+	return nil
+}
+func (stubChannel) Capabilities() Capability { return Capability{Text: true} }
+
+func TestRegisterLookup(t *testing.T) {
+	Register("stub", func(ChannelConfig, Handler) (Channel, error) {
+		return stubChannel{}, nil
+	})
+	fn, ok := Lookup("stub")
+	if !ok {
+		t.Fatal("expected factory")
+	}
+	ch, err := fn(ChannelConfig{}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ch.Type() != "stub" {
+		t.Fatalf("type=%s", ch.Type())
+	}
+}