refactor(auth): modularize auth plugin with physical subpackages and decoupled services

backend/plugins/domain/auth/model/do/oauth_state_test.go

@@ -0,0 +1,32 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package do_test
+
+import (
+	"Wavelet/plugins/domain/auth/model/do"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestOAuthStatePayload(t *testing.T) {
+	payload := do.OAuthStatePayload{
+		SourceName:  "github",
+		Purpose:     "login",
+		UserID:      12345,
+		SessionHash: "hash-abc-123",
+	}
+
+	encoded, err := payload.Encode()
+	require.NoError(t, err)
+	assert.NotEmpty(t, encoded)
+
+	decoded, err := do.DecodeOAuthStatePayload(encoded)
+	require.NoError(t, err)
+	assert.Equal(t, payload, decoded)
+
+	_, err = do.DecodeOAuthStatePayload("invalid-json")
+	assert.Error(t, err)
+}