diff --git a/src/agent/backtestRunner.ts b/src/agent/backtestRunner.ts
index e91de2c..7f7a3e0 100644
--- a/src/agent/backtestRunner.ts
+++ b/src/agent/backtestRunner.ts
@@ -3,7 +3,7 @@ import { loadConfig } from "../config/loader.js";
 import { getDb } from "../storage/db.js";
 import { getBacktestBroker } from "../broker/index.js";
 import { getStockOhlcv, getIndexOhlcv, type Bar } from "../data/sources/dnsePublic.js";
-import { DISCOVERY_UNIVERSE, discoverTickers } from "../tools/discover.js";
+import { DISCOVERY_UNIVERSE, discoverTickers, mapLimit } from "../tools/discover.js";
 import { setActiveAsOf } from "./clock.js";
 import { runTeamAnalysis } from "./team/index.js";
 import type { FinalDecision, TeamEvent } from "./team/state.js";
@@ -259,10 +259,12 @@ export async function runBacktestSession(
   const fetchFrom = startSec - 7 * 86400;
   const fetchTo = endSec + 7 * 86400;
   const bars: Record<string, Bar[]> = {};
-  for (const t of universe) {
+
+  await mapLimit(universe, 10, async (t) => {
     bars[t] = await getStockOhlcv(t, "30", fetchFrom, fetchTo);
     if (cb.signal?.aborted) throw new Error("aborted");
-  }
+  });
+
   const vnindex = await getIndexOhlcv("VNINDEX", "30", fetchFrom, fetchTo);
 
   const intervalTurns = intervalCloses(vnindex, startSec, endSec, interval.minutes);
diff --git a/src/data/sources/dnsePublic.ts b/src/data/sources/dnsePublic.ts
index 151733c..3fb4f31 100644
--- a/src/data/sources/dnsePublic.ts
+++ b/src/data/sources/dnsePublic.ts
@@ -47,7 +47,7 @@ async function fetchOhlcs(
 
 export function seriesToBars(s: OhlcvSeries): Bar[] {
   const out: Bar[] = [];
-  for (let i = 0; i < s.t.length; i++) {
+  for (let i = 0; i < (s.t?.length || 0); i++) {
     if (s.c[i] == null) continue; // skip empty intraday slots
     out.push({
       time: s.t[i]!,
diff --git a/src/tools/discover.ts b/src/tools/discover.ts
index 413e476..4f7b9a2 100644
--- a/src/tools/discover.ts
+++ b/src/tools/discover.ts
@@ -285,7 +285,7 @@ async function resolveUniverse(
   return { universe: "all_listed", tickers: await listedTickers(["HOSE", "HNX", "UPCOM"]) };
 }
 
-async function mapLimit<T, R>(
+export async function mapLimit<T, R>(
   items: readonly T[],
   concurrency: number,
   fn: (item: T) => Promise<R>,