Refactor message sending architecture and implement legacy driver support

- Removed UniversalMessageSender from group_generator.py and private_generator.py.
- Updated PlatformIOManager to manage legacy send drivers and ensure send pipeline readiness.
- Enhanced LegacyPlatformDriver to utilize prepared messages for sending.
- Refactored send_service to unify message sending logic and integrate with Platform IO.
- Added regression tests for Platform IO legacy driver and send service functionality.

pytests/test_platform_io_legacy_driver.py

@@ -0,0 +1,124 @@
+"""Platform IO legacy driver 回归测试。"""
+
+from typing import Any, Dict, Optional
+
+import pytest
+
+from src.chat.utils import utils as chat_utils
+from src.chat.message_receive import uni_message_sender
+from src.platform_io.drivers.base import PlatformIODriver
+from src.platform_io.drivers.legacy_driver import LegacyPlatformDriver
+from src.platform_io.manager import PlatformIOManager
+from src.platform_io.types import DeliveryReceipt, DeliveryStatus, DriverDescriptor, DriverKind, RouteBinding, RouteKey
+
+
+class _PluginDriver(PlatformIODriver):
+    """测试用插件发送驱动。"""
+
+    def __init__(self, driver_id: str, platform: str) -> None:
+        """初始化测试驱动。
+
+        Args:
+            driver_id: 驱动 ID。
+            platform: 负责的平台名称。
+        """
+        super().__init__(
+            DriverDescriptor(
+                driver_id=driver_id,
+                kind=DriverKind.PLUGIN,
+                platform=platform,
+                plugin_id="test.plugin",
+            )
+        )
+
+    async def send_message(
+        self,
+        message: Any,
+        route_key: RouteKey,
+        metadata: Optional[Dict[str, Any]] = None,
+    ) -> DeliveryReceipt:
+        """返回一个固定成功回执。
+
+        Args:
+            message: 待发送消息。
+            route_key: 当前路由键。
+            metadata: 发送元数据。
+
+        Returns:
+            DeliveryReceipt: 固定成功回执。
+        """
+        del metadata
+        return DeliveryReceipt(
+            internal_message_id=str(message.message_id),
+            route_key=route_key,
+            status=DeliveryStatus.SENT,
+            driver_id=self.driver_id,
+            driver_kind=self.descriptor.kind,
+        )
+
+
+@pytest.mark.asyncio
+async def test_platform_io_uses_legacy_driver_when_no_explicit_send_route(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """没有显式发送路由时，应由 Platform IO 回退到 legacy driver。"""
+    manager = PlatformIOManager()
+    monkeypatch.setattr(chat_utils, "get_all_bot_accounts", lambda: {"qq": "bot-qq"})
+
+    try:
+        await manager.ensure_send_pipeline_ready()
+
+        fallback_drivers = manager.resolve_drivers(RouteKey(platform="qq"))
+        assert [driver.driver_id for driver in fallback_drivers] == ["legacy.send.qq"]
+
+        plugin_driver = _PluginDriver(driver_id="plugin.qq.sender", platform="qq")
+        await manager.add_driver(plugin_driver)
+        manager.bind_send_route(
+            RouteBinding(
+                route_key=RouteKey(platform="qq"),
+                driver_id=plugin_driver.driver_id,
+                driver_kind=plugin_driver.descriptor.kind,
+            )
+        )
+
+        explicit_drivers = manager.resolve_drivers(RouteKey(platform="qq"))
+        assert [driver.driver_id for driver in explicit_drivers] == ["plugin.qq.sender"]
+    finally:
+        await manager.stop()
+
+
+@pytest.mark.asyncio
+async def test_legacy_platform_driver_uses_prepared_universal_sender(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """legacy driver 应复用已预处理消息的旧链发送函数。"""
+    calls: list[dict[str, Any]] = []
+
+    async def _fake_send_prepared_message_to_platform(message: Any, show_log: bool = True) -> bool:
+        """记录 legacy driver 调用。"""
+        calls.append({"message": message, "show_log": show_log})
+        return True
+
+    monkeypatch.setattr(
+        uni_message_sender,
+        "send_prepared_message_to_platform",
+        _fake_send_prepared_message_to_platform,
+    )
+
+    driver = LegacyPlatformDriver(
+        driver_id="legacy.send.qq",
+        platform="qq",
+        account_id="bot-qq",
+    )
+    message = type("FakeMessage", (), {"message_id": "message-1"})()
+    receipt = await driver.send_message(
+        message=message,
+        route_key=RouteKey(platform="qq"),
+        metadata={"show_log": False},
+    )
+
+    assert len(calls) == 1
+    assert calls[0]["message"] is message
+    assert calls[0]["show_log"] is False
+    assert receipt.status == DeliveryStatus.SENT
+    assert receipt.driver_id == "legacy.send.qq"