chore: import upstream snapshot with attribution

examples/stories/streaming/server_lowlevel.py

@@ -0,0 +1,69 @@
+"""Progress, in-flight logging, and cancellation against the low-level Server."""
+
+from typing import Any
+
+import anyio
+import mcp_types as types
+
+from mcp.server.context import ServerRequestContext
+from mcp.server.lowlevel import Server
+from stories._hosting import run_server_from_args
+
+COUNTDOWN_INPUT_SCHEMA: dict[str, Any] = {
+    "type": "object",
+    "properties": {"steps": {"type": "integer"}},
+    "required": ["steps"],
+}
+
+
+def build_server() -> Server[Any]:
+    async def list_tools(
+        ctx: ServerRequestContext[Any], params: types.PaginatedRequestParams | None
+    ) -> types.ListToolsResult:
+        return types.ListToolsResult(
+            tools=[
+                types.Tool(
+                    name="countdown",
+                    description="Emit one progress + one log notification per step; observes cancellation.",
+                    input_schema=COUNTDOWN_INPUT_SCHEMA,
+                )
+            ]
+        )
+
+    async def call_tool(ctx: ServerRequestContext[Any], params: types.CallToolRequestParams) -> types.CallToolResult:
+        assert params.name == "countdown" and params.arguments is not None
+        steps = int(params.arguments["steps"])
+        try:
+            for i in range(1, steps + 1):
+                await ctx.session.report_progress(float(i), float(steps), f"step {i}/{steps}")
+                await ctx.session.send_notification(
+                    types.LoggingMessageNotification(
+                        params=types.LoggingMessageNotificationParams(
+                            level="info", logger="countdown", data=f"step {i}/{steps}"
+                        )
+                    ),
+                    related_request_id=ctx.request_id,
+                )
+        except anyio.get_cancelled_exc_class():
+            raise
+        return types.CallToolResult(
+            content=[types.TextContent(text=f"completed {steps}/{steps}")],
+            structured_content={"completed": steps, "total": steps},
+        )
+
+    async def set_logging_level(
+        ctx: ServerRequestContext[Any], params: types.SetLevelRequestParams
+    ) -> types.EmptyResult:
+        """Registered so the server advertises the `logging` capability; never called."""
+        raise NotImplementedError
+
+    return Server(  # pyright: ignore[reportDeprecated]
+        "streaming-example",
+        on_list_tools=list_tools,
+        on_call_tool=call_tool,
+        on_set_logging_level=set_logging_level,
+    )
+
+
+if __name__ == "__main__":
+    run_server_from_args(build_server)