fix(dogfood): ignore zombie-only process groups on macOS

[BleedingDev]

Summary

• let macOS EPERM process-group probes fall through to the existing zombie-aware inspection
• keep live non-zombie process groups classified as running
• close the fixture pipe deterministically

Why

On BSD/macOS, killpg can return EPERM for a process group containing only zombies. Treating that as unconditional liveness makes bounded dogfood cleanup report a false surviving-process failure.

Verification

• portable process suite: 13 passed
• dogfood output validator suite: 13 passed
• Python compile and diff checks pass
• branch scope audit: one commit, two script files, clean worktree

Supports #707.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 00d564b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-30T15:32:04.913549Z	00d564b	PR opened

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.