chore: import upstream snapshot with attribution

examples/stories/parallel_calls/server.py

@@ -0,0 +1,31 @@
+"""One tool that rendezvouses with named peers, proving the server dispatches calls concurrently."""
+
+from collections import defaultdict
+
+import anyio
+
+from mcp.server.mcpserver import Context, MCPServer
+from stories._hosting import run_server_from_args
+
+
+def build_server() -> MCPServer:
+    mcp = MCPServer("parallel-calls-example")
+    # One Event per tag, shared across every call to this server instance. A handler sets its
+    # own tag's event, then waits for every peer's — so no call can return until all named
+    # peers are concurrently in-flight. A sequential dispatcher would deadlock here.
+    arrivals: dict[str, anyio.Event] = defaultdict(anyio.Event)
+
+    @mcp.tool()
+    async def meet(tag: str, party: list[str], ctx: Context) -> str:
+        """Signal arrival as `tag`, block until every tag in `party` has also arrived, then return."""
+        arrivals[tag].set()
+        for peer in party:
+            await arrivals[peer].wait()
+        await ctx.report_progress(1.0, total=1.0, message=tag)
+        return tag
+
+    return mcp
+
+
+if __name__ == "__main__":
+    run_server_from_args(build_server)