⚡ Bolt: [performance improvement] optimize cache key generation by avoiding Date allocations

.jules/bolt.md

@@ -35,3 +35,9 @@
 **Learning:** When generating a bounded, deduplicated subset (Set) from an array in hot paths, avoid array method chains like `Array.from(new Set([...arr1, ...arr2.map(f)])).slice(0, N)`. This causes several intermediate array allocations that create significant GC pressure during long loops (e.g., historical backtests).
 **Action:** Use an empty `Set` along with bounded `for` loops and a results array that implement an early exit (`tickers.length < maxCandidates`) to directly stream unique items. This processes fewer elements and generates zero intermediate arrays.
 
+## 2024-05-15 - DNSE API returns null instead of empty arrays
+**Learning:** The DNSE API (entrade.com.vn) returns `{ t: null, c: null }` instead of `{ t: [], c: [] }` when there is no data (e.g. for weekends/holidays). Attempting to read `.length` on `t` throws a TypeError inside `seriesToBars` that can abort the entire backtest runner.
+**Action:** Always verify if API arrays from external sources exist (`if (!s.t) return []`) before iterating, even if the TypeScript interface implies they are arrays.
+## 2024-05-15 - Fast cache keys using integer math
+**Learning:** Calling `new Date().toISOString().slice()` in hot paths (like `cached()` key generation during a backtest loop) adds up significantly (~1ms per thousand calls).
+**Action:** When grouping cache keys by day, use fast integer math `Math.floor(unixSecs / 86400)` instead of string-based date allocations to maintain identical semantics while avoiding object instantiation.

src/data/cache.ts

@@ -41,7 +41,10 @@ export function resetCacheStats() {
  */
 function namespaced(key: string): string {
   if (asOfClock.getStore()?.asOfSec != null || isAsOfOverridden()) {
-    const day = new Date(nowSec() * 1000).toISOString().slice(0, 10);
+    // ⚡ Bolt: Optimize cache key generation by replacing slow Date/String
+    // allocations (new Date(...).toISOString().slice(0, 10)) with integer math,
+    // grouping by UTC day since epoch to maintain the same invalidation semantics.
+    const day = Math.floor(nowSec() / 86400);
     return `asof=${day}|${key}`;
   }
   return key;

src/data/sources/dnsePublic.ts

@@ -46,6 +46,7 @@ async function fetchOhlcs(
 }
 
 export function seriesToBars(s: OhlcvSeries): Bar[] {
+  if (!s.t) return [];
   const out: Bar[] = [];
   for (let i = 0; i < s.t.length; i++) {
     if (s.c[i] == null) continue; // skip empty intraday slots