fix(sys): handle EACCES from fstat on socketpair fds

[springmin]

On some Linux configurations (notably with SELinux), fstat() on socketpair fds returns EACCES. Fall back to a zeroed stat instead of erroring.

[claude]

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[coderabbitai]

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• src/sys/lib.rs

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Walkthrough

On Linux/Android, fstat now treats EACCES from the syscall as a special case: it probes the FD with getsockopt(SO_TYPE) and returns a zero-initialized Stat if the probe succeeds; other errors are returned as before.

Changes

fstat EACCES special-case handling

Layer / File(s)	Summary
fstat: EACCES probe and zeroed Stat return src/sys/lib.rs	fstat now matches on syscall errors: on EACCES it runs getsockopt(SO_TYPE) and returns a zero-initialized Stat if that probe succeeds; other errno values are converted to Error::from_code_int(e, Tag::fstat) as before.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is incomplete; it lacks the required 'How did you verify your code works?' section from the template.	Add a 'How did you verify your code works?' section describing testing or verification of the EACCES handling logic.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: handling EACCES errors from fstat on socketpair file descriptors.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/sys/lib.rs`:
- Around line 2098-2103: The current fstat error handling swallows Err(e) if e
== libc::EACCES for any Fd and returns a zeroed stat; restrict that fallback to
socket descriptors only by adding a platform-gated helper (e.g.
is_socket_fd(fd)) that uses getsockopt(SOL_SOCKET, SO_TYPE) on linux/android to
detect sockets, then change the Err(e) branch in the fstat handling so that if e
== libc::EACCES you call is_socket_fd(fd) and only return Ok(zeroed stat) when
true, otherwise propagate Err(Error::from_code_int(e, Tag::fstat)); ensure the
helper is inlined and only compiled on the appropriate targets and reference the
existing Tag::fstat and fstat handling code paths when making the change.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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• src/sys/lib.rs

[springmin]

Updated: fstat EACCES fallback is now scoped to socket fds only via getsockopt(SO_TYPE) probe. Non-socket fds will properly propagate the EACCES error.