feat：优化timing门控逻辑，减少消耗，提高速度

src/maisaka/builtin_tool/finish.py

@@ -0,0 +1,34 @@
+"""finish 内置工具。"""
+
+from typing import Optional
+
+from src.core.tooling import ToolExecutionContext, ToolExecutionResult, ToolInvocation, ToolSpec
+
+from .context import BuiltinToolRuntimeContext
+
+
+def get_tool_spec() -> ToolSpec:
+    """获取 finish 工具声明。"""
+
+    return ToolSpec(
+        name="finish",
+        brief_description="结束本轮思考，等待后续新的外部消息再继续。",
+        provider_name="maisaka_builtin",
+        provider_type="builtin",
+    )
+
+
+async def handle_tool(
+    tool_ctx: BuiltinToolRuntimeContext,
+    invocation: ToolInvocation,
+    context: Optional[ToolExecutionContext] = None,
+) -> ToolExecutionResult:
+    """执行 finish 内置工具。"""
+
+    del context
+    tool_ctx.runtime._enter_stop_state()
+    return tool_ctx.build_success_result(
+        invocation.tool_name,
+        "当前对话循环已结束本轮思考，等待新的外部消息到来。",
+        metadata={"pause_execution": True},
+    )