Harden PR Description Updater against one-shot safe-output exhaustion

[Copilot]

The PR Description Updater could consume its single allowed update_pull_request call with probe/placeholder content, then fail to apply the real synthesized description due to max: 1. This change tightens the workflow prompt so the one-shot update is reserved for the final body only.

• Prompt contract for one-shot PR updates

  • Step 4 now requires exactly one update_pull_request call, using only the final synthesized markdown body.
  • Explicitly forbids probe/test/placeholder updates (for example "-").

• Failure-path behavior

  • If a final complete body is not available, the workflow now instructs the agent to emit report_incomplete instead of calling update_pull_request.
  • Clarifies no retry behavior for update_pull_request within the same run.

• Compiled workflow sync

  • Regenerated pr-description-caveman.lock.yml to match updated markdown workflow source.

### Step 4 — Update the PR

Call `update_pull_request` exactly once with the final synthesised markdown body.

Do NOT send probe/test/placeholder content (for example `"-"`) ...
If you cannot produce the final complete body, call `report_incomplete` and do not call `update_pull_request`.

• Fixes [aw] PR Description Updater reported incomplete result #49438

[Copilot]

Pull request overview

Hardens the PR Description Updater so its one permitted PR update is reserved for the final synthesized description.

Changes:

• Prohibits probe, placeholder, and retry updates.
• Uses report_incomplete when no complete body is available.
• Synchronizes the compiled workflow metadata.

Show a summary per file

File	Description
.github/workflows/pr-description-caveman.md	Strengthens the one-shot update contract.
.github/workflows/pr-description-caveman.lock.yml	Updates the generated body hash.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced

[github-actions]

🎉 This pull request is included in a new release.

Release: v0.84.2