Fixed concurrency issue in MetaDb chunk expansion

[michaelstaib]

Fixes #9500

[Copilot]

Pull request overview

Addresses a concurrency hazard in ResultDocument.MetaDb chunk-array expansion by preventing pooled chunk buffers from being returned while they may still be observed by concurrent readers, and adds an integration regression test intended to cover the large paging + DataLoader scenario.

Changes:

• Retain the previous _chunks buffer across expansions and only return it to the pool on the next expansion or Dispose.
• Introduce a volatile cursor value (_nextValue) to provide an atomic/read-friendly cursor snapshot for readers.
• Add a new integration test that pages 100,000 nodes and resolves a composite DataLoader field with a wide selection set.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/HotChocolate/Core/test/Execution.Tests/Integration/DataLoader/Issue9500Tests.cs	Adds a large paging + DataLoader integration test aimed at reproducing the reported failure mode.
src/HotChocolate/Core/src/Types/Text/Json/ResultDocument.MetaDb.cs	Prevents premature ArrayPool returns during chunk-array expansion; adds an atomic cursor snapshot for concurrent readers.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (6a3b7a3) to head (cfdf02e).
⚠️ Report is 1080 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #9508       +/-   ##
==========================================
- Coverage   74.16%       0   -74.17%     
==========================================
  Files        2677       0     -2677     
  Lines      140790       0   -140790     
  Branches    16371       0    -16371     
==========================================
- Hits       104421       0   -104421     
+ Misses      30774       0    -30774     
+ Partials     5595       0     -5595     

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