fix: ensure GC safety for arena-allocated string values

[jensneuse]

Summary by CodeRabbit

• Performance & Reliability

  • Improved error handling to enhance system stability and reliability when processing GraphQL errors, subgraph errors, authorization edge cases, and rate limiting scenarios.

• Tests

  • Added comprehensive benchmark tests validating robustness across error handling scenarios including fetch errors, invalid responses, subgraph errors, authorization rejections, and rate limiting.

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes refactor memory allocation in JSON value handling to ensure arena-based GC safety by replacing direct AST parsing with arena-allocated helper functions, and introduce comprehensive benchmark tests validating the arena allocation across multiple error scenarios.

Changes

Cohort / File(s)	Summary
Arena-based string allocation refactoring v2/pkg/engine/resolve/loader.go	Introduced parseStringOnArena and stringValueOnArena helper functions for GC-safe arena allocation. Systematically replaced ~20+ direct AST JSON parsing and string value creation calls to use these helpers throughout error construction, path rewriting, and error extension handling.
Arena GC safety benchmarks v2/pkg/engine/resolve/loader_arena_gc_test.go	Added comprehensive benchmark suite exercising arena allocation across diverse error paths: fetch errors, invalid JSON/shape, subgraph errors (wrap/passthrough modes), error codes, service-name augmentation, and authorization/rate-limit rejections. Includes helper data source and test response constructors with explicit GC invocations.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: ensure GC safety for arena-allocated string values' directly summarizes the main change - introducing arena allocation helpers and updating string/JSON value creations to use arena allocation for garbage collection safety.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into master

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/arena-alloc-panic

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