gate-miss: PR #309 native launchd lifecycle coverage #310

PR: #309
Found at: pre-merge
Signal: review
Defect: The initial LaunchAgent could kill the embedding worker after sync exited because AbandonProcessGroup was absent; Ubuntu CI also does not exercise the native launchd lifecycle.
Expected check: none
Class: automatable
Conversion: Add a macOS native fixture check on the next scheduler change, covering worker survival, install/reload, absolute program arguments, loaded-status exit codes, and uninstall cleanup.

The defect is fixed in this PR, with a plist assertion and independent process-group evidence. Final native fixtures covered pending, zero, and nonzero exit codes and cleanup. Mac-only plist roundtrips are not run by Ubuntu CI. Another interval after the first kickstart, sleep/logout behavior, and an executable moved after installation were not exercised; those remain platform acceptance cases, not demonstrated defects.