chore: import upstream snapshot with attribution

examples/stories/error_handling/server_lowlevel.py

@@ -0,0 +1,45 @@
+"""Two error channels on lowlevel.Server: return is_error=True yourself, or raise MCPError."""
+
+from typing import Any
+
+import mcp_types as types
+
+from mcp.server.context import ServerRequestContext
+from mcp.server.lowlevel import Server
+from mcp.shared.exceptions import MCPError
+from stories._hosting import run_server_from_args
+
+_TOOLS = [
+    types.Tool(name="divide", description="Divide a by b.", input_schema={"type": "object"}),
+    types.Tool(name="restricted", description="Always rejects.", input_schema={"type": "object"}),
+]
+
+
+def build_server() -> Server[Any]:
+    async def list_tools(
+        ctx: ServerRequestContext[Any], params: types.PaginatedRequestParams | None
+    ) -> types.ListToolsResult:
+        return types.ListToolsResult(tools=_TOOLS)
+
+    async def call_tool(ctx: ServerRequestContext[Any], params: types.CallToolRequestParams) -> types.CallToolResult:
+        args = params.arguments or {}
+        if params.name == "divide":
+            a, b = float(args["a"]), float(args["b"])
+            if b == 0:
+                # Execution error: build the is_error result yourself.
+                return types.CallToolResult(
+                    content=[types.TextContent(text="cannot divide by zero")],
+                    is_error=True,
+                )
+            return types.CallToolResult(content=[types.TextContent(text=str(a / b))])
+        if params.name == "restricted":
+            # Protocol error: raise MCPError; the dispatcher serialises it as a
+            # JSON-RPC error response with this code/message/data.
+            raise MCPError(code=types.INVALID_PARAMS, message="this tool is gated", data={"reason": "demo"})
+        raise MCPError(code=types.INVALID_PARAMS, message=f"Unknown tool: {params.name}")
+
+    return Server("error-handling-example", on_list_tools=list_tools, on_call_tool=call_tool)
+
+
+if __name__ == "__main__":
+    run_server_from_args(build_server)