feat: restructure client-side code

public/js/ws.js

@@ -0,0 +1,35 @@
+import { state } from './state.js';
+
+let ws;
+let reconnectAttempts = 0;
+let reconnectTimer = null;
+const outbox = [];
+
+export function wsIsOpen() { return ws && ws.readyState === WebSocket.OPEN; }
+export function sendMsg(obj) { if (wsIsOpen()) ws.send(JSON.stringify(obj)); else outbox.push(obj); }
+
+function scheduleReconnect(connect) {
+  if (reconnectTimer) return;
+  const delay = Math.min(30000, 1000 * Math.pow(2, reconnectAttempts));
+  reconnectAttempts++;
+  reconnectTimer = setTimeout(() => { reconnectTimer = null; connect(); }, delay);
+}
+
+export function connectWS(onMessage) {
+  const url = (location.protocol === 'https:' ? 'wss://' : 'ws://') + location.host;
+  ws = new WebSocket(url);
+  ws.addEventListener('open', () => {
+    reconnectAttempts = 0;
+    setTimeout(() => { while (outbox.length && wsIsOpen()) { try { ws.send(JSON.stringify(outbox.shift())); } catch { break; } } }, 100);
+  });
+  ws.addEventListener('message', (ev) => onMessage(ev));
+  ws.addEventListener('close', () => { scheduleReconnect(() => connectWS(onMessage)); });
+  ws.addEventListener('error', () => { try { ws.close(); } catch {} });
+}
+
+window.addEventListener('online', () => {
+  if (!wsIsOpen()) {
+    if (reconnectTimer) { clearTimeout(reconnectTimer); reconnectTimer = null; }
+    // Kick off a reconnect by calling connectWS from app main again
+  }
+});