feat(logger): update logger configuration to set log level to Fatal to eliminate IO lock contention

fix(redis): silence Redis internal logging and optimize connection pool settings to reduce mutex contention

feat(userlist): enhance user list component with avatar support and improved styling

test(load): add production-style load test script for WebSocket connections and Redis PubSub stress testing

chore(loadtest): create script to run load tests with pprof profiling for performance analysis

loadtest/loadtest_redis_stress.js

@@ -0,0 +1,120 @@
+import { check, sleep } from "k6";
+import { Counter, Rate, Trend } from "k6/metrics";
+import ws from "k6/ws";
+
+// =============================================================================
+// CUSTOM METRICS (avoid conflicts with k6's built-in ws_* metrics)
+// =============================================================================
+const connectionTime = new Trend("ws_connection_time_ms");
+const messageRTT = new Trend("ws_message_rtt_ms");
+const connectionsFailed = new Counter("ws_connections_failed");
+const messagesReceived = new Counter("ws_msgs_received");
+const messagesSent = new Counter("ws_msgs_sent");
+const connectionSuccess = new Rate("ws_connection_success");
+
+// =============================================================================
+// 1000 USERS TEST - STRESS REDIS PUBSUB SUBSCRIPTIONS
+// =============================================================================
+export const options = {
+  stages: [
+    { duration: "20s", target: 20 }, // Warmup: 20 users
+    { duration: "10s", target: 200 }, // Ramp to 200
+    { duration: "10s", target: 500 }, // Ramp to 500
+    { duration: "10s", target: 1000 }, // Ramp to 1000
+    { duration: "60s", target: 1000 }, // Hold at 1000 for 1 minute
+    { duration: "10s", target: 0 }, // Ramp down
+  ],
+
+  thresholds: {
+    ws_connection_time_ms: ["p(95)<500"], // Target: <500ms connection
+    ws_message_rtt_ms: ["p(95)<100"], // Target: <100ms message RTT
+    ws_connection_success: ["rate>0.95"], // Target: >95% success rate
+  },
+};
+
+export default function () {
+  // CRITICAL: Create unique room per user to stress Redis PubSub
+  // This creates ~1000 subscriptions (1 per room) to trigger the bottleneck
+  const roomId = `loadtest-room-${__VU}`;
+  const url = `ws://localhost:8080/ws/loadtest/${roomId}`;
+
+  const connectStart = Date.now();
+
+  const res = ws.connect(url, {}, function (socket) {
+    const connectDuration = Date.now() - connectStart;
+    connectionTime.add(connectDuration);
+    connectionSuccess.add(1);
+
+    // Send realistic Yjs-sized messages (200 bytes)
+    // Yjs sync messages are typically 100-500 bytes
+    const payload = new Uint8Array(200);
+    payload[0] = 1; // Message type: Yjs sync
+
+    // Fill with realistic data (not zeros)
+    for (let i = 1; i < 200; i++) {
+      payload[i] = Math.floor(Math.random() * 256);
+    }
+
+    socket.on("message", (data) => {
+      messagesReceived.add(1);
+    });
+
+    socket.on("error", (e) => {
+      connectionsFailed.add(1);
+    });
+
+    // Send message every 1 second (realistic collaborative edit rate)
+    socket.setInterval(function () {
+      socket.sendBinary(payload.buffer);
+      messagesSent.add(1);
+    }, 1000);
+
+    // Keep connection alive for 100 seconds (longer than test duration)
+    socket.setTimeout(function () {
+      socket.close();
+    }, 100000);
+  });
+
+  const connectCheck = check(res, {
+    "WebSocket connected": (r) => r && r.status === 101,
+  });
+
+  if (!connectCheck) {
+    connectionsFailed.add(1);
+    connectionSuccess.add(0);
+  }
+
+  // Small sleep to avoid hammering connection endpoint
+  sleep(0.1);
+}
+
+export function setup() {
+  console.log("========================================");
+  console.log("  Redis PubSub Stress Test: 1000 Users");
+  console.log("========================================");
+  console.log("⚠️  CRITICAL: Creates ~1000 rooms");
+  console.log("   This stresses Redis PubSub subscriptions");
+  console.log("   Each room = 1 dedicated PubSub connection");
+  console.log("========================================");
+  console.log("Expected bottleneck (before fix):");
+  console.log("  - 58.96s in PubSub health checks");
+  console.log("  - 28.09s in ReceiveTimeout");
+  console.log("  - Connection success rate: 80-85%");
+  console.log("  - P95 latency: 20-26 seconds");
+  console.log("========================================");
+  console.log("Expected after fix:");
+  console.log("  - <1s in PubSub operations");
+  console.log("  - Connection success rate: >95%");
+  console.log("  - P95 latency: <500ms");
+  console.log("========================================");
+}
+
+export function teardown(data) {
+  console.log("========================================");
+  console.log("  Load Test Completed");
+  console.log("========================================");
+  console.log("Check profiling data with:");
+  console.log("  curl http://localhost:8080/debug/pprof/mutex > mutex.pb");
+  console.log("  go tool pprof -top mutex.pb");
+  console.log("========================================");
+}