[wieslawsoltes]

Problem and change

The 50,000-node NodeIterator gate shared a long-lived engine with the full suite and could abort under Windows PartitionAlloc during teardown.

This test-only layer runs the unchanged 50,001-visit assertions on a fresh engine, records native DOM, wrapper-handle, and V8 heap bounds before destruction, and destroys the fixture immediately after measurement. Production runtime and allocator behavior are unchanged.

Closes #85. The equivalent test change remains in draft consolidation PR #76.

Cumulative validation

• Implementation layer a459e0fd; exact cumulative head d84a6a6f
• Release V8 native engine build
• Focused DOMPurify/filter contract: 10/10 local passes
• Isolated 50,000-node performance and memory gate: 5/5 passes at 406-437 ms wall time
• Gate requires 50,001 visits/filter calls, zero construction-time filter calls, under 5 seconds, bounded linear scaling, at most 70,000 native nodes and wrapper handles, and at most 128 MiB V8 heap
• Required TreeWalker/NodeIterator profile: 6/6 subtests
• Required unchanged removal-during-filtering WPT: 4/4 subtests
• git diff --check
• Remote validation runs only on this cumulative top to minimize CI and artifacts

Native GitHub stack #158

1. Implement NodeIterator for DOM traversal #127 — NodeIterator implementation (Implement NodeIterator for DOMPurify and Code OSS chat rendering #82)
2. Isolate the NodeIterator stress fixture #129 — current cumulative top — isolated scaling and memory gate (Isolate 50k NodeIterator stress fixture from Windows PartitionAlloc suite state #85)

Merge both layers atomically through Stack #158 after the current-head related check passes.