diff --git a/app/backend/src/redis.ts b/app/backend/src/redis.ts
new file mode 100644
index 0000000..83fefa4
--- /dev/null
+++ b/app/backend/src/redis.ts
@@ -0,0 +1,22 @@
+// Single Redis client for the whole backend (sessions, rate-limit, view buffer).
+// Lazy-connected so test suites can swap it out before connection.
+import { Redis } from 'ioredis';
+import { config } from './config.js';
+
+export const redis = new Redis(config.REDIS_URL, {
+  lazyConnect: true,
+  // Reconnect with exponential backoff up to 5s; ioredis handles command queuing while reconnecting.
+  retryStrategy: (times: number) => Math.min(times * 200, 5000),
+  enableReadyCheck: true,
+});
+
+redis.on('error', (err: Error) => {
+  // Don't crash on transient errors — Fastify will surface 503s via /health.
+  console.error('[redis]', err.message);
+});
+
+export async function connectRedis() {
+  if (redis.status === 'wait' || redis.status === 'end') {
+    await redis.connect();
+  }
+}