[codex] Dedupe PatchDeck agent command comments

[jeremymcs]

Summary

• Suppress duplicate public PatchDeck agent-command comments for retries on the same PR head SHA.
• Keep first-run visibility and log skipped duplicates under github.agent-command.
• Add regression coverage for same-head retry dedupe.

Root Cause

PatchDeck posted a fresh top-level "started an automated PR update" comment every time automatic PR work retried, even when the branch head had not changed and a previous agent run had already posted the same public command marker.

Verification

• npm run check
• node --import tsx --test server/babysitter.test.ts --test-name-pattern "same-head retries"

Notes

• Earlier npm run test still had two unrelated failures: server/packagedBundle.test.ts expected no node:sqlite external, and server/storage.test.ts hit the existing SQLite lock recovery failure. The new babysitter regression passed in that full run.

[github-actions]

📄 Documentation Review Reminder

This PR changes source files but does not update any public documentation.

Changed source files:

server/babysitter.test.ts
server/babysitter.ts

Please check if documentation in docs/public/ needs to be updated:

• No documentation update needed
• Documentation updated in this PR
• Follow-up documentation issue created

Public docs are Markdown files in docs/public/. They are automatically
rendered to HTML and deployed to GitHub Pages when merged to main.

Available docs: getting-started.md, pr-babysitter.md, agent-dispatch.md, configuration.md, pr-questions.md