修改了nanobot，往Hermes agent的风格走，进度1/3

app-instance/backend/beaver/tools/builtins/echo.py

@@ -0,0 +1,43 @@
+"""最小调试工具：把输入原样回显。
+
+它的价值不是业务能力，而是运行时验证：
+当你只想确认 tool loop 是否能走通时，`echo` 是最便宜、最确定的测试工具。
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+
+ECHO_TOOL_DESCRIPTION = "Echo the provided text back to the agent. Useful for verifying tool calling."
+
+ECHO_TOOL_PARAMETERS: dict[str, Any] = {
+    "type": "object",
+    "properties": {
+        "text": {
+            "type": "string",
+            "description": "The text to echo back.",
+        }
+    },
+    "required": ["text"],
+}
+
+
+def echo_tool(*, text: str) -> str:
+    return text
+
+
+@dataclass(slots=True)
+class EchoTool:
+    """面向 runtime 的最小内建工具。"""
+
+    name: str = "echo"
+    description: str = ECHO_TOOL_DESCRIPTION
+    parameters: dict[str, Any] = field(default_factory=lambda: dict(ECHO_TOOL_PARAMETERS))
+
+    async def execute(self, **kwargs: Any) -> str:
+        text = kwargs.get("text")
+        if not isinstance(text, str):
+            raise ValueError("echo tool requires a string field 'text'")
+        return echo_tool(text=text)