Harden PR-gate verification and lifecycle

[screenleon]

Summary

• Harden PR-gate synthesis, reviewer protocol, and assurance verification.
• Make detached supervisor and parent-operation lifecycle failures explicit and recoverable.
• Tighten PM command-guard parsing and bounded scope expansion.
• Add schema, lifecycle, operation, guard, and publication-race regression coverage.

Validation

• pmctl gate wait gate-20260731-080812-c7b94f --cd /home/screenleon/github/pm-dispatch
• Final gate verdict: GO
• Gate artifact and assurance: verified
• Guard, operation, lifecycle, schema, docstring, and focused publication-race suites passed.

Impact

This change prevents malformed or tampered gate artifacts from being published, preserves diagnosable terminal state after supervisor or producer failures, and keeps destructive-command checks fail-closed without blocking safe quoted search data.