ws: WebSocketServer.clients is undefined (should be a Set) — heartbeat loops kill the process #9325

Summary

WebSocketServer.clients is undefined under Perry, where node has a
Set. Any for…of over it throws TypeError: is not iterable, and because
the idiomatic place to iterate it is a heartbeat setInterval, the throw lands
in a timer callback where application code cannot catch it — the process exits
and, under systemd, restart-loops with no traffic at all.

Perry 0.5.1519 from source plus the fixes in #9314 and #9319. ws 8.x,
Linux x86_64.

Repro

import { WebSocketServer } from "ws";

const wss = new WebSocketServer({ port: 0 });
console.log("clients  =", Object.prototype.toString.call(wss.clients));
console.log("iterator =", typeof (wss.clients as any)?.[Symbol.iterator]);
try {
  let n = 0;
  for (const _c of wss.clients) n += 1;
  console.log("iterated", n, "— OK");
} catch (e) {
  console.log("THREW:", String(e));
}

The server object is otherwise constructed — the constructor returns, and
other members work; only clients is missing.

How it presents in a real service

This is the standard ws heartbeat, straight from the library's own docs:

const heartbeat = setInterval(() => {
  for (const ws of wss.clients) {        // ← throws here
    if (!alive.has(ws)) { ws.terminate(); continue; }
    alive.delete(ws);
    ws.ping();
  }
}, heartbeatMs);

Our API dies every few seconds on this, with no requests involved. It took
a gdb backtrace to find, because the JS-level message is only
TypeError: is not iterable at <anonymous> even with --debug-symbols:

#0  perry_runtime::symbol::iterator::throw_value_not_iterable ()
#1  js_get_iterator ()
#2  perry_closure_apps_api_src_ws_attach_ts ()
#3  js_interval_timer_tick ()
#4  perry_runtime::promise::microtasks::run_microtasks ()
#5  main ()

Why it is worth prioritising

• Uncatchable. It throws inside a timer callback in library-idiomatic
  code, so no try/catch in application code prevents the exit.
• No traffic needed. A service with zero connections still dies on the
  heartbeat, so it looks like a startup or config problem rather than a
  missing property.
• wss.clients is how every ws server does connection tracking, heartbeats
  and broadcast — it is not a corner of the API.

A clear TypeError on access would already be a large improvement over an
undefined that only fails later, at a distance, inside a timer.