diff --git a/core/agent/protocols.py b/core/agent/protocols.py
new file mode 100644
index 0000000..258feaf
--- /dev/null
+++ b/core/agent/protocols.py
@@ -0,0 +1,45 @@
+"""Agent 专属 Protocol 端口。"""
+from __future__ import annotations
+
+from typing import Any, Protocol, runtime_checkable
+
+import pluggy
+
+from core.agent.types import LoopResult, Step
+
+hookspec = pluggy.HookspecMarker("agent_loop")
+hookimpl = pluggy.HookimplMarker("agent_loop")
+
+
+@runtime_checkable
+class ToolDispatcher(Protocol):
+    """Agent 工具调度端口。无效工具名抛 ValueError。"""
+
+    async def dispatch(
+        self, tool_name: str, args: dict[str, Any], *, context: dict[str, Any]
+    ) -> str: ...
+
+
+class AgentLoopSpec:
+    """AgentLoop 生命周期扩展点。
+
+    每个 hookimpl 可选择观察（返回 None）或变换（返回值）。
+    """
+
+    @hookspec
+    async def before_step(
+        self, iteration: int, messages: list[dict[str, Any]]
+    ) -> None: ...
+
+    @hookspec
+    async def after_tool(
+        self, iteration: int, step: Step
+    ) -> str | None: ...
+
+    @hookspec
+    async def after_step(
+        self, iteration: int, messages: list[dict[str, Any]]
+    ) -> None: ...
+
+    @hookspec
+    async def on_finish(self, result: LoopResult) -> None: ...
diff --git a/tests/unit/test_agent_protocols.py b/tests/unit/test_agent_protocols.py
new file mode 100644
index 0000000..306a878
--- /dev/null
+++ b/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