feat(agent): add host policy foundation (#6273)

app/agent/middleware/policy.py

@@ -0,0 +1,72 @@
+"""LangChain 工具调用的 MoviePilot 宿主策略中间件。"""
+
+from collections.abc import Awaitable, Callable
+from typing import Any
+
+from langchain.agents.middleware import AgentMiddleware, ToolCallRequest
+
+from app.agent.policy import (
+    DEFAULT_TOOL_POLICY_ORCHESTRATOR,
+    AgentToolPolicyOrchestrator,
+    ToolPolicyContext,
+    call_policy_hook,
+)
+
+
+class AgentPolicyMiddleware(AgentMiddleware):
+    """观测进入本地 ToolNode 的 client-side 工具调用和结果。
+
+    模型供应商原生 server tools 在供应商侧执行，不经过本地 middleware，
+    因而不具备这里生成的 start/finish/fail 回执。
+    """
+
+    def __init__(
+        self,
+        *,
+        context: ToolPolicyContext,
+        orchestrator: AgentToolPolicyOrchestrator = DEFAULT_TOOL_POLICY_ORCHESTRATOR,
+    ) -> None:
+        """绑定宿主可信上下文和共享策略编排器。"""
+        self.context = context
+        self.orchestrator = orchestrator
+
+    async def awrap_tool_call(
+        self,
+        request: ToolCallRequest,
+        handler: Callable[[ToolCallRequest], Awaitable[Any]],
+    ) -> Any:
+        """在 handler 外层生成 shadow 决策和 secret-safe 回执摘要。"""
+        tool_call = request.tool_call or {}
+        arguments = tool_call.get("args") or {}
+        if not isinstance(arguments, dict):
+            arguments = {}
+        observation = call_policy_hook(
+            "start",
+            self.orchestrator.start,
+            context=self.context,
+            tool=request.tool,
+            arguments=arguments,
+            invocation_id=tool_call.get("id"),
+        )
+        try:
+            result = await handler(request)
+        except Exception as error:
+            if observation is not None:
+                call_policy_hook(
+                    "fail",
+                    self.orchestrator.fail,
+                    observation,
+                    error,
+                )
+            raise
+        if observation is not None:
+            call_policy_hook(
+                "finish",
+                self.orchestrator.finish,
+                observation,
+                result,
+            )
+        return result
+
+
+__all__ = ["AgentPolicyMiddleware"]