addition of new dashboard

backend/modules/dashboard/cache.js

@@ -0,0 +1,33 @@
+import { getPool } from "../../db/index.js";
+
+// Lockless: concurrent cold misses may both compute, last writer wins.
+export async function getCached(userId, tag, ttlMs, compute) {
+  let client = await getPool();
+  try {
+    const hit = (
+      await client.query(
+        `SELECT data FROM cache
+         WHERE user_id = $1 AND tag = $2
+           AND updated_ts > NOW() - ($3 * interval '1 millisecond')`,
+        [userId, tag, ttlMs],
+      )
+    ).rows[0];
+    if (hit) return hit.data;
+  } finally {
+    await client.release();
+  }
+
+  const data = await compute();
+
+  client = await getPool();
+  try {
+    await client.query(
+      `INSERT INTO cache (user_id, tag, data) VALUES ($1, $2, $3::jsonb)
+       ON CONFLICT (user_id, tag) DO UPDATE SET data = EXCLUDED.data, updated_ts = NOW()`,
+      [userId, tag, data],
+    );
+  } finally {
+    await client.release();
+  }
+  return data;
+}