Reject oversized bytearray resize requests - #9815

Summary

Reject bytearray resize requests above CPython 3.15's normal GIL-build bytes allocation limit before allocating. Keep same-size no-ops and exported-buffer errors ahead of the allocation check.

The failure appeared after #9807 enabled test_bytes.test_resize. On 32-bit WASI, the existing Vec-backed implementation can successfully allocate sys.maxsize bytes. I reproduced that on a pre-#9813 build; the bytearray source is identical on current main and the failing #9813 CI merge.

The fix is seven Rust lines. The snippet covers the first forbidden length on either pointer width, preservation of contents, and BufferError precedence. No Lib tests or workflow settings change.

Reference: CPython 3.15 bytearray size ceiling and resize ordering, resize implementation.

Validation

• Exact CI WASI profile/features build with Rust 1.99.0 and Wasmer 7.5.0.
• WASI test_bytes: 332 tests, 18 skipped, success. Focused resize selection: 2 tests passed.
• WASI boundary probe: six allocation-limit checks and eighteen error-precedence checks passed, including the first forbidden 32-bit length, 2147483631.
• CPython 3.15.1: full modified bytearray snippet and the same boundary/error-precedence probe passed.
• Independent source review, formatting, diff checks, and repository pre-commit hooks passed.
• Native workspace tests, C-API tests, strict Clippy, native test_bytes, and snippet harness are queued behind existing shared builds. This remains a draft until those checks and CI finish.

AI assistance: OpenAI Codex investigated, implemented, reviewed, and tested this change. The runtime did not expose an exact model version.