Short title (summary)

Return CAPACITY for oversize DOM allocation in parse flow

Description

• Added an explicit bound check in document::allocate to return CAPACITY when the requested size exceeds SIMDJSON_MAXSIZE_BYTES.

• Previously, oversized declared input lengths could reach allocation and return MEMALLOC, which misclassifies a capacity-limit violation as an allocation failure.

• This ensures consistent error semantics: invalid sizes return CAPACITY, while real allocation failures continue to return MEMALLOC.

• Issue reproduced: parsing with a declared length larger than the supported DOM capacity returns incorrect error classification.

Type of change

• Bug fix
• Optimization
• New feature
• Refactor / cleanup
• Documentation / tests
• Other (please describe):

How to verify / test

• Added regression test: parser_parse_huge_declared_length_capacity
  • Uses parser.parse(...) with declared length SIMDJSON_MAXSIZE_BYTES + 1
  • Verifies that the parser returns CAPACITY
• Test exercises real parse flow (parse → ensure_capacity → document::allocate)
• Designed to be CI-safe:
  • Uses std::string input to avoid compiler object-size warnings (-Werror)
  • Includes guard to prevent overflow on 32-bit platforms

Run locally:

cmake -B build -D SIMDJSON_DEVELOPER_MODE=ON
cmake --build build
ctest --test-dir build

Checklist before submitting
- [x] I added/updated tests covering my change (if applicable)
- [x] Code builds locally and passes my check
- [ ] Documentation / README updated if needed
- [x] Commits are atomic and messages are clear
- [ ] I linked the related issue (if applicable)

Final notes
- Change is intentionally minimal and limited to error classification for oversized inputs.
-No impact on valid parsing behaviour.
-Test is structured to be portable and stable across compilers and architectures.