feat(core/agent): 添加 ToolDispatcher Protocol 和 AgentLoopSpec hookspec

ToolDispatcher async + context 参数。AgentLoopSpec 四个 async 生命周期 hook。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/test_agent_protocols.py

@@ -0,0 +1,30 @@
+"""core/agent/protocols.py 单元测试。"""
+from __future__ import annotations
+
+from typing import Any
+
+import pluggy
+
+from core.agent.protocols import AgentLoopSpec, ToolDispatcher
+
+
+class _FakeDispatcher:
+    async def dispatch(
+        self, tool_name: str, args: dict[str, Any], *, context: dict[str, Any]
+    ) -> str:
+        return f"executed {tool_name}"
+
+
+def test_fake_dispatcher_satisfies_protocol() -> None:
+    assert isinstance(_FakeDispatcher(), ToolDispatcher)
+
+def test_plain_object_not_dispatcher() -> None:
+    assert not isinstance(object(), ToolDispatcher)
+
+def test_hookspec_can_register() -> None:
+    pm = pluggy.PluginManager("agent_loop")
+    pm.add_hookspecs(AgentLoopSpec)
+    assert pm.hook.before_step is not None
+    assert pm.hook.after_tool is not None
+    assert pm.hook.after_step is not None
+    assert pm.hook.on_finish is not None