feat: add takeover service core logic

Implement TakeoverService for avatar takeover chat feature:
- check_takeover_enabled: query Authorization for enabled takeover
- generate_reply: call local chat API via httpx to generate responses
- execute_takeover: get owner IM credentials, generate reply, send via BoxIM
- enqueue_delayed_message: Redis delayed queue with graceful degradation
- process_delayed_queue: placeholder for scheduled worker

Service degrades gracefully when Redis is unavailable.

digital-avatar-app/backend/tests/test_takeover_service.py

@@ -0,0 +1,136 @@
+"""Tests for the TakeoverService — message listening, decision, reply execution."""
+import pytest
+from unittest.mock import AsyncMock, patch, MagicMock
+from services.takeover_service import TakeoverService
+from models import Authorization
+
+
+@pytest.fixture
+def mock_db():
+    db = MagicMock()
+    return db
+
+
+@pytest.fixture
+def mock_boxim():
+    client = AsyncMock()
+    client.get_credentials.return_value = {"accid": "owner_acc", "token": "tok"}
+    client.send_p2p_message.return_value = True
+    return client
+
+
+@pytest.fixture
+def mock_auth():
+    auth = MagicMock(spec=Authorization)
+    auth.takeover_enabled = True
+    auth.takeover_mode = "immediate"
+    auth.takeover_delay_seconds = 30
+    auth.avatar_id = "avatar_123"
+    auth.target_id = "target_user_123"
+    auth.owner_id = "owner_huihui_123"
+    return auth
+
+
+def test_check_takeover_enabled_returns_auth_when_enabled(mock_db, mock_auth, mock_boxim):
+    mock_db.query.return_value.filter.return_value.filter.return_value.first.return_value = mock_auth
+    service = TakeoverService(mock_db, mock_boxim)
+    result = service.check_takeover_enabled("owner_123", "target_123")
+    assert result == mock_auth
+
+
+def test_check_takeover_enabled_returns_none_when_disabled(mock_db, mock_boxim):
+    disabled_auth = MagicMock(spec=Authorization)
+    disabled_auth.takeover_enabled = False
+    mock_db.query.return_value.filter.return_value.filter.return_value.first.return_value = disabled_auth
+    service = TakeoverService(mock_db, mock_boxim)
+    result = service.check_takeover_enabled("owner_123", "target_123")
+    assert result is None
+
+
+@pytest.mark.asyncio
+async def test_generate_reply_returns_answer(mock_boxim):
+    mock_db = MagicMock()
+    with patch("services.takeover_service.httpx.AsyncClient") as mock_client_class:
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"code": 200, "data": {"answer": "Hello back"}}
+        mock_client_class.return_value.__aenter__.return_value.post.return_value = mock_response
+
+        service = TakeoverService(mock_db, mock_boxim)
+        result = await service.generate_reply("avatar_123", "Hello")
+        assert result == "Hello back"
+
+
+@pytest.mark.asyncio
+async def test_execute_takeover_success(mock_db, mock_boxim, mock_auth):
+    with patch("services.takeover_service.httpx.AsyncClient") as mock_client_class:
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"code": 200, "data": {"answer": "Hello back"}}
+        mock_client_class.return_value.__aenter__.return_value.post.return_value = mock_response
+
+        service = TakeoverService(mock_db, mock_boxim)
+        message = {"from_accid": "user_acc", "content": "Hello"}
+
+        result = await service.execute_takeover(mock_auth, message)
+
+        assert result is True
+        mock_boxim.get_credentials.assert_called_once()
+        mock_boxim.send_p2p_message.assert_called_once()
+
+
+def test_enqueue_delayed_message_with_redis(mock_db, mock_boxim, mock_auth):
+    mock_redis = MagicMock()
+    service = TakeoverService(mock_db, mock_boxim, mock_redis)
+    message = {"msg_id": "msg_1", "from_accid": "user_acc", "content": "Hello"}
+
+    service.enqueue_delayed_message(mock_auth, message)
+
+    mock_redis.setex.assert_called_once()
+
+
+def test_enqueue_delayed_message_without_redis_logs_warning(mock_db, mock_boxim, mock_auth):
+    """When Redis is not configured, enqueue_delayed_message should log a warning and not crash."""
+    service = TakeoverService(mock_db, mock_boxim)
+    message = {"msg_id": "msg_1", "from_accid": "user_acc", "content": "Hello"}
+
+    # Should not raise
+    service.enqueue_delayed_message(mock_auth, message)
+
+
+@pytest.mark.asyncio
+async def test_execute_takeover_fails_when_no_credentials(mock_db, mock_boxim, mock_auth):
+    """execute_takeover should return False when boxim.get_credentials returns None."""
+    mock_boxim.get_credentials.return_value = None
+    service = TakeoverService(mock_db, mock_boxim)
+    message = {"from_accid": "user_acc", "content": "Hello"}
+
+    result = await service.execute_takeover(mock_auth, message)
+
+    assert result is False
+
+
+@pytest.mark.asyncio
+async def test_generate_reply_handles_empty_answer(mock_boxim):
+    """generate_reply should return empty string when answer is missing."""
+    mock_db = MagicMock()
+    with patch("services.takeover_service.httpx.AsyncClient") as mock_client_class:
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"code": 200, "data": {}}
+        mock_client_class.return_value.__aenter__.return_value.post.return_value = mock_response
+
+        service = TakeoverService(mock_db, mock_boxim)
+        result = await service.generate_reply("avatar_123", "Hello")
+        assert result == ""
+
+
+@pytest.mark.asyncio
+async def test_generate_reply_handles_error_code(mock_boxim):
+    """generate_reply should return empty string when API returns error code."""
+    mock_db = MagicMock()
+    with patch("services.takeover_service.httpx.AsyncClient") as mock_client_class:
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"code": 500, "message": "Internal error"}
+        mock_client_class.return_value.__aenter__.return_value.post.return_value = mock_response
+
+        service = TakeoverService(mock_db, mock_boxim)
+        result = await service.generate_reply("avatar_123", "Hello")
+        assert result == ""