diff --git a/.jules/bolt.md b/.jules/bolt.md
index b08b203a..6f68589b 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.
+## 2026-07-15 - Optimize array and map operations in tight loops
+**Learning:** Using `Array.prototype.reduce`/`forEach` and `Map` incurs significant callback allocation, garbage collection, and hash-lookup overhead in hot paths (like `computeTaskMetrics`).
+**Action:** Replace them with standard `for` loops and `Float64Array`/`Int32Array` when processing lists sequentially and caching numeric primitive values.
diff --git a/app.js b/app.js
index a04aae71..cfbb41e4 100644
--- a/app.js
+++ b/app.js
@@ -1370,21 +1370,27 @@ 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 tasks = state.tasks;
+  const len = tasks.length;
+  // ⚡ Bolt: Use Float64Array and for loop to avoid JS engine object allocation, GC, and hash-lookup overhead.
+  const durationCache = new Float64Array(len);
+  let totalDays = 0;
+
+  for(let i = 0; i < len; i++) {
+    const task = tasks[i];
     const duration = calculateDurationDays(task.plannedStartDate, task.plannedEndDate);
-    durationCache.set(task.id, duration);
-    return sum + duration;
-  }, 0);
+    durationCache[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 < len; i++) {
+    const task = tasks[i];
+    const durationDays = durationCache[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 +1414,7 @@ function computeTaskMetrics() {
       plannedDateWarning,
       actualDateWarning
     });
-  });
+  }
 
   return {
     totalDays,