diff --git a/.jules/bolt.md b/.jules/bolt.md
index b08b203a..dc5437ea 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -4,3 +4,6 @@
 ## 2026-07-12 - Optimize renderTaskRow DOM allocations
 **Learning:** Caching unattached template nodes and instantiating them via `.cloneNode(false)` reduces DOM instantiation overhead in O(N) render loops significantly.
 **Action:** Apply this optimization to other hot-path rendering elements such as rows, cells, and stack containers.
+## 2026-08-16 - Use Int32Array and standard loops instead of Map and array methods
+**Learning:** In hot loops, allocating callbacks for reduce/forEach and using Map incurs overhead due to GC and hash-lookup.
+**Action:** Use Int32Array caching and standard for loops for measurable optimizations.
diff --git a/app.js b/app.js
index a04aae71..1d20a282 100644
--- a/app.js
+++ b/app.js
@@ -1370,21 +1370,26 @@ function validateDateRange(startLabel, startValue, endLabel, endValue, errors) {
 }
 
 function computeTaskMetrics() {
-  // ⚡ Bolt: Cache durationDays during total calculation to avoid recalculating for every task
-  const durationCache = new Map();
-  const totalDays = state.tasks.reduce((sum, task) => {
-    const duration = calculateDurationDays(task.plannedStartDate, task.plannedEndDate);
-    durationCache.set(task.id, duration);
-    return sum + duration;
-  }, 0);
+  const tasks = state.tasks;
+  const numTasks = tasks.length;
+  // ⚡ Bolt: Use standard for-loop and Int32Array to eliminate callback allocation and Map overhead in O(N) loop
+  const durations = new Int32Array(numTasks);
+  let totalDays = 0;
+
+  for (let i = 0; i < numTasks; i++) {
+    const duration = calculateDurationDays(tasks[i].plannedStartDate, tasks[i].plannedEndDate);
+    durations[i] = duration;
+    totalDays += duration;
+  }
 
   const baseDate = state.baseDate;
   const byTask = new Map();
   let totalWeightedPlannedRatio = 0;
   let totalWeightedActualRatio = 0;
 
-  state.tasks.forEach((task) => {
-    const durationDays = durationCache.get(task.id);
+  for (let i = 0; i < numTasks; i++) {
+    const task = tasks[i];
+    const durationDays = durations[i];
     const weightRatio = totalDays > 0 ? durationDays / totalDays : 0;
     const plannedProgressRatio = calculatePlannedProgressRatio(baseDate, task.plannedStartDate, task.plannedEndDate, durationDays);
     const actualProgressRatio = (ACTUAL_PROGRESS_MAP[task.actualProgressStatus] || 0) / 100;
@@ -1408,7 +1413,7 @@ function computeTaskMetrics() {
       plannedDateWarning,
       actualDateWarning
     });
-  });
+  }
 
   return {
     totalDays,