fix(process): honor cancellation at bounded file read completion - #8908

Problem

readBoundedFileBytes returns an empty success for an already-aborted zero-byte expected read. It also returns success or overflow when cancellation arrives during the final asynchronous read, because cancellation is checked only before I/O.

Changes

Check the caller's abort signal after option validation and after each successful read, before interpreting EOF, expected-size completion, or overflow. Preserve the caller's exact abort reason and existing cancellationFailure mapping. The caller continues to own and close the file handle.

This fixes the shared file-read boundary without changing the admitted byte limit or expected-size read semantics.

Validation

• tests/boundary/filesystem/boundedFileBytes.test.ts: 10 passed on Node 24.22.1 / Vitest 5.0.3, with a focused external test configuration.
• Real temporary-file cases cover an already-aborted zero-byte read and cancellation during EOF, early EOF, expected-size completion, and overflow, alongside exact-limit and growing-file controls.
• Re-running against the unmodified source: 5 failed, 5 passed.
• Targeted TypeScript 5.9.3 checking, repository-pinned oxfmt 0.72.0 formatting, and git diff --check passed.

The full project checks and provider workflows were not run.

Author readiness

Human owner: @Afloat16

• I reviewed the final diff and relevant existing code, understand the change and its edge cases, and take responsibility for the complete PR, including AI-assisted work.
• I checked the evidence above, confirmed it supports the current change, and recorded meaningful validation gaps.
• I declare this PR ready for initial maintainer review.