⚡ Bolt: Optimize array density validation in shared-types

.jules/bolt.md

@@ -42,6 +42,10 @@
 **Learning:** Using `Array.from(map.values()).map(...)` creates an unnecessary intermediate array which wastes memory allocation and garbage collection time, particularly for frequently re-rendered components handling large collections.
 **Action:** Use a `for...of` loop over `map.values()` to iterate and push mapped elements directly into the final array for O(1) memory and avoiding intermediate array allocations.
 
+## 2026-07-09 - [Array density check optimization]
+**Learning:** [Using Array.from().every() to check for array density creates O(N) intermediate array allocations which add unnecessary garbage collection overhead on the critical path.]
+**Action:** [Use a standard for-loop with an early return (i in value) for an O(1) memory and faster check.]
+
 ## 2026-03-12 - O(1) early exit for confidence level
 **Learning:** Using `.reduce()` unconditionally iterates over the entire array for operations with an absolute bound (e.g. finding if there's any 'low' confidence section).
 **Action:** Replace unconditional `.reduce()` with a `for...of` loop and early `break` to short-circuit upon finding the minimum possible bound, changing O(N) worst-case into an O(K) best-case execution, yielding measurable performance gains on large documents.

packages/shared-types/src/index.ts

@@ -388,7 +388,14 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 
 /** Documented. */
 function isDenseArray(value: unknown): value is unknown[] {
-  return Array.isArray(value) && Array.from({ length: value.length }, (_, index) => index in value).every(Boolean);
+  if (!Array.isArray(value)) return false;
+  // Performance: Avoid O(N) allocation of intermediate array from Array.from()
+  for (let i = 0; i < value.length; i++) {
+    if (!(i in value)) {
+      return false;
+    }
+  }
+  return true;
 }
 
 /** Documented. */