Fix websocket backend URL for HF Space deployments

frontend/lib/websocket.ts

@@ -0,0 +1,35 @@
+const BACKEND_URL = (process.env.NEXT_PUBLIC_BACKEND_URL || "http://localhost:8000").replace(/\/$/, "")
+
+export function createSimulationSocket(
+  simulationId: string,
+  onMessage: (msg: any) => void,
+  onError: () => void
+) {
+  const wsBase = BACKEND_URL.replace(/^http:/, "ws:").replace(/^https:/, "wss:")
+  const wsUrl = `${wsBase}/ws/${simulationId}`
+  
+  const ws = new WebSocket(wsUrl)
+  
+  ws.onmessage = (event) => {
+    try {
+      const msg = JSON.parse(event.data)
+      // DEBUG: surface incoming websocket payload for troubleshooting
+      try { console.debug("WS_RECV", msg) } catch (e) {}
+      onMessage(msg)
+    } catch (e) {
+      console.error("Failed to parse WebSocket message:", e)
+    }
+  }
+  
+  ws.onerror = (error) => {
+    console.error("WebSocket error:", error)
+    onError()
+  }
+  
+  ws.onclose = (event) => {
+    console.log("WebSocket closed", { code: event.code, reason: event.reason })
+    onError()
+  }
+  
+  return ws
+}