Stabilize doctor process cancellation test

[lynnswap]

Purpose

Prevent timing-dependent failures in cancellingLiveRunnerTerminatesTheDoctorProcess, which failed in the ReviewMonitor CI job. The PID file can exist before its contents are written, and assertion reporting can change errno before the next assertion reads it. The CI log does not identify the failing assertion, so the exact failure remains unconfirmed.

Changes

• Install the signal handler and write the PID before publishing readiness. Stop at the existing deadline if readiness never arrives.
• Use exec /bin/sleep to keep the same PID without consuming a CPU core while waiting for cancellation.
• Stop and join the watchdog when it is cancelled, and fail the test if it had to send SIGKILL.
• Capture the kill result and errno immediately, before running assertions.

Testing

• Final changes: all 15 CodexCommandUpdateCheckerTests tests passed on Xcode 27 / macOS arm64, including 17 executions with parameterized cases.
• git diff --check passed.
• Local Codex reviews reported no findings.

Command used for the final test run:

xcodebuild test \
  -project Tools/ReviewMonitor/CodexReviewMonitor.xcodeproj \
  -scheme CodexReviewMonitor \
  -destination 'platform=macOS,arch=arm64' \
  -disableAutomaticPackageResolution \
  -onlyUsePackageVersionsFromResolvedFile \
  -skipMacroValidation \
  -only-testing:CodexReviewMonitorCITests/CodexCommandUpdateCheckerTests \
  CODE_SIGNING_ALLOWED=NO \
  CODE_SIGNING_REQUIRED=NO

[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 2026-10-03T10:37:35.800510Z	202399b	PR opened
🔒 Security Review	✅ Completed 2026-10-03T10:38:45.740312Z	202399b	PR opened

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