test(facts): the subtree count's deep-chain test builds its 20,000-deep chain on the packed store, as a scan does - the reference store keeps every node's whole path, about 1.2 GB of the 2 GB heap GitHub's macOS runner gives Node, for a count that reads none of them (CI4 sweep)

Found by the CI4 sweep for tests that could run a 2 GB heap out. "a deep
chain does not overflow the stack" built its chain with ObjectScanStore
(the oracle), whose addNode joins each node's path from its parent's and
keeps it - endsWith copies the parent's whole path, so every node held its
own, the depth squared: the file's peak was 1,427 MB resident, and under a
1 GB heap it died with the same "Reached heap limit" in
String.prototype.endsWith -> StringSlowFlatten as CI run 39095045009.
Under CI's 2 GB it passed with a little over half the heap to spare.

buildCountTable reads only isDir, forEachChild and count, the same on
either store, so the property is unchanged: 20,000 folders deep, the one
file and every folder counted, no stack frame per level. Now 258 MB peak,
and the whole file passes under a 1 GB heap. The reference store's own
deep build is not what this test is about, and production keeps it only to
wrap trees that already carry a path on every node.

Mutant: buildCountTable made recursive - RED, "RangeError: Maximum call
stack size exceeded", before and after the change; restored and checked by
SHA-256.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: Prithvi-Web

tests/subtreeCount.test.ts

@@ -80,7 +80,11 @@ test('an empty folder is 0 files — and a file is 1, never 0', () => {
 test('a deep chain does not overflow the stack', () => {
   // Recursion is the obvious implementation and it dies on real input: a
   // node_modules chain or a Time Machine backup nests far deeper than this.
-  const store = new ObjectScanStore('/root', '/', dirIn('root'));
+  // Built on the packed store, as a scan is (CI4): the reference store keeps
+  // every node's whole path, about 1.2 GB down a 20,000-deep chain — over
+  // half the 2 GB heap GitHub's macOS runner gives Node, and nothing to do
+  // with the count, which reads only isDir and forEachChild.
+  const store = new PackedScanStore('/root', '/', dirIn('root'));
   let cursor = store.rootId;
   const DEPTH = 20_000;
   for (let i = 0; i < DEPTH; i++) cursor = store.addNode(cursor, dirIn(`d${String(i)}`));