Fix finish_child Err arm to fall through to teardown

[Finesssee]

Follow-up to #398. The Err arm in finish_child's poll loop early-returned None before the teardown block, so a transient try_wait error (e.g. ECHILD) skipped kill+wait - leaving the child unreaped (zombie on Unix) and reporting a false discovery failure. Now falls through to the same kill+wait+recover teardown as grace expiry. Closes the last error-path gap from the #396 review.

Summary by CodeRabbit

• Bug Fixes
  • Improved command cleanup when checking a process’s exit status encounters a temporary error.
  • Ensured teardown proceeds reliably instead of ending without an exit code.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fe76ace6-2cd8-4e6e-a5e0-8a0424bbd29b

📥 Commits

Reviewing files that changed from the base of the PR and between 1f6f524 and cb9b701.

📒 Files selected for processing (1)

• rust/src/host/command_runner.rs

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📝 Walkthrough

Walkthrough

finish_child now proceeds with process teardown when try_wait returns an error. The teardown comments document transient wait errors, including ECHILD and handle races.

Changes

Process teardown handling

Layer / File(s)	Summary
Wait error teardown behavior rust/src/host/command_runner.rs	finish_child exits the grace loop on try_wait errors and proceeds with process teardown. The comments document transient wait errors as teardown triggers.

Estimated code review effort: 2 (Simple) | ~5 minutes

Merge Risk: ⚪ Minimal · up to cb9b7

This narrowly changes error handling so child teardown runs instead of returning early; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: making the finish_child error path fall through to teardown.
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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✨ Finishing Touches 💡 2

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🛠️ Fix failing CI checks 💡

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/finish-child-err-fallthrough

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