⚡ 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.]
+
 ## 2026-07-08 - Vectorize SSM novelty extraction
 **Learning:** Extracting checkerboard kernel responses one diagonal window at a time repeats Python slicing and summation overhead for every SSM frame.
 **Action:** Sum each checkerboard offset across the full valid diagonal with `np.diagonal(...)`, and keep a loop-reference parity test so boundary scoring stays numerically stable.

packages/shared-types/src/index.ts

@@ -388,7 +388,18 @@ 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 Array.from() allocation while keeping a one-time length boundary.
+  const arrayLength = Number(value.length);
+  if (!Number.isSafeInteger(arrayLength) || arrayLength < 0 || arrayLength > 0xffffffff) {
+    return false;
+  }
+  for (let i = 0; i < arrayLength; i++) {
+    if (!(i in value)) {
+      return false;
+    }
+  }
+  return true;
 }
 
 /** Documented. */

packages/shared-types/test/index.test.ts

@@ -113,6 +113,83 @@ describe("shared type helpers", () => {
     expect(() => parseProjectSummary({ ...validSummary, extraField: true })).toThrow("extraField");
   });
 
+  it("snapshots array length while validating dense array boundaries", () => {
+    let lengthReads = 0;
+    let entriesStarted = false;
+    const supportedAudioFormats = new Proxy(["wav"], {
+      get(target, property, receiver) {
+        if (property === "entries") {
+          entriesStarted = true;
+        }
+        if (property === "length") {
+          lengthReads += 1;
+          return !entriesStarted && lengthReads > 1 ? 2 : Reflect.get(target, property, receiver);
+        }
+        return Reflect.get(target, property, receiver);
+      }
+    }) as ProjectSummary["supportedAudioFormats"];
+    const summary: ProjectSummary = {
+      id: "project-1",
+      title: "Demo Song",
+      status: "running",
+      supportedAudioFormats
+    };
+
+    expect(validateProjectSummary(summary)).toBeNull();
+  });
+
+  it("rejects array proxies with non-primitive changing lengths", () => {
+    let lengthCoercions = 0;
+    const changingLength = {
+      valueOf() {
+        lengthCoercions += 1;
+        return lengthCoercions === 1 ? 2 : 0;
+      }
+    };
+    const supportedAudioFormats = new Proxy(["wav"], {
+      get(target, property, receiver) {
+        if (property === "length") {
+          return changingLength;
+        }
+        return Reflect.get(target, property, receiver);
+      }
+    }) as ProjectSummary["supportedAudioFormats"];
+    const summary: ProjectSummary = {
+      id: "project-1",
+      title: "Demo Song",
+      status: "running",
+      supportedAudioFormats
+    };
+
+    expect(validateProjectSummary(summary)).toBe(
+      "Invalid project summary contract: invalid field 'supportedAudioFormats'"
+    );
+    expect(lengthCoercions).toBe(1);
+  });
+
+  it("rejects array proxies with non-finite or out-of-range lengths", () => {
+    for (const length of [Number.POSITIVE_INFINITY, 0xffffffff + 1, 1.5]) {
+      const supportedAudioFormats = new Proxy(["wav"], {
+        get(target, property, receiver) {
+          if (property === "length") {
+            return length;
+          }
+          return Reflect.get(target, property, receiver);
+        }
+      }) as ProjectSummary["supportedAudioFormats"];
+      const summary: ProjectSummary = {
+        id: "project-1",
+        title: "Demo Song",
+        status: "running",
+        supportedAudioFormats
+      };
+
+      expect(validateProjectSummary(summary)).toBe(
+        "Invalid project summary contract: invalid field 'supportedAudioFormats'"
+      );
+    }
+  });
+
   it("property-checks supported local audio sources", () => {
     fc.assert(
       fc.property(