Fix incomplete WebSocket close handshake in Workers (error 1101)

The server side of a WebSocketPair never echoed the client's close
frame, so workerd detected a hung connection that would never generate
a response.  Add server.close() in the close handler per Cloudflare's
documented pattern, and add a test asserting wasClean === true.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jmorrell

src/__tests__/workers.workers.test.ts

@@ -156,6 +156,25 @@ describe("Workers runtime integration tests", () => {
   });
 
   describe("WebSocket functionality in Workers", () => {
+    it("should complete close handshake when client disconnects", async () => {
+      const response = await SELF.fetch("http://localhost/rpc", {
+        method: "GET",
+        headers: { Upgrade: "websocket" },
+      });
+
+      const ws = response.webSocket!;
+      ws.accept();
+
+      const closeEvent = new Promise<CloseEvent>((resolve) => {
+        ws.addEventListener("close", (event) => resolve(event as CloseEvent));
+      });
+
+      ws.close(1000, "normal closure");
+
+      const event = await closeEvent;
+      expect(event.wasClean).toBe(true);
+    });
+
     it("should upgrade WebSocket connection with 101 response", async () => {
       const response = await SELF.fetch("http://localhost/rpc", {
         method: "GET",

src/websocket.ts

@@ -113,6 +113,14 @@ export function newWorkersWebSocketRpcSession<
   const [client, server] = Object.values(pair);
   server.accept();
 
+  // Complete the WebSocket close handshake when the client disconnects.
+  // Without this workerd detects a hung connection that will never
+  // generate a response (error 1101).
+  // https://developers.cloudflare.com/workers/observability/errors/
+  server.addEventListener("close", () => {
+    server.close();
+  });
+
   const transport = createWebSocketTransport(server);
   const session = new RpcSession<TRemote, TLocal>(transport, service ?? ({} as TLocal), {
     role: "acceptor",