Add regression for malformed root writes

[vladar]

Summary

• add a focused regression for a malformed query result that assigns the same normalized key to the operation root and a nested entity
• demonstrate that a later write replacing the nested entity with null reaches the two-root-chunk invariant

Testing

The new regression intentionally fails on the current implementation with:

Invariant violation: Failed to update "query ConsumerNodeByIdQuery": expected a single root chunk, got 2

[github-actions]

📊 Benchmark Analysis Report

✅ No significant performance changes detected

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Threshold: 5% change

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Updated: 2026-07-13T13:05:33.178Z