feat: Validate PR action posts results as PR comment, passing-checks label, and auto-update outdated branches

[Copilot]

Three enhancements to the CI/automation workflows: validation results are now posted directly on the PR (not just in the Actions summary), a passing-checks label is applied/removed based on check outcome, and outdated challenge PR branches are automatically rebased onto the base branch.

validate-pr.yml

• PR comment: validation report is written to /tmp/pr_validation_summary.md; a new step creates or updates a single bot comment on the PR with the full report on every run
• passing-checks label: new step adds the label on validation success, removes it on failure; creates the label via GET-then-POST (no duplicate creation, logs all outcomes)
• Added issues: write permission; id: validate on the validation step for outcome referencing

review-challenge-prs.yml

• Linked PR entries: all summary list items now use [#N](url) markdown links instead of plain #N
• passing-checks label: addPassingLabel/removePassingLabel helpers called in every branch — added for clean PRs, removed for noReview, changesRequested, and actionableComments states; label created once before the loop
• Auto-update outdated branches: at the top of each PR iteration, pulls.get reads mergeable_state; calls updateBranch when 'behind'; separate try/catch for check vs. update with distinct error messages; all mergeable_state values documented; updated PRs appear in a new 🔀 Branch Updated summary section
• Added contents: write permission

PR Checklist

1. Select Contribution Type

• Kit (kits/<category>/<kit-name>/)
• Bundle (bundles/<bundle-name>/)
• Template (templates/<template-name>/)

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2. General Requirements

• PR is for one project only (no unrelated changes)
• No secrets, API keys, or real credentials are committed
• Folder name uses kebab-case and matches the flow ID
• All changes are documented in README.md (purpose, setup, usage)

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3. File Structure (Check what applies)

• config.json present with valid metadata (name, description, tags, steps, author, env keys)
• All flows in flows/<flow-name>/ (where applicable) include:
  • config.json (Lamatic flow export)
  • inputs.json
  • meta.json
  • README.md
• .env.example with placeholder values only (kits only)
• No hand‑edited flow config.json node graphs (changes via Lamatic Studio export)

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4. Validation

• npm install && npm run dev works locally (kits: UI runs; bundles/templates: flows are valid)
• PR title is clear (e.g., [kit] Add <name> for <use case>)
• GitHub Actions workflows pass (all checks are green)
• All CodeRabbit or other PR review comments are addressed and resolved
• No unrelated files or projects are modified

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[github-actions]

PR Validation Results

Check Results

Check	Status
No edits to existing projects	✅ Pass
Required root files present	✅ Pass
Flow folder structure valid	✅ Pass
No changes outside contribution dirs	⚠️ Warning

Warnings

• ⚠️ File outside kits/bundles/templates modified: .github/workflows/review-challenge-prs.yml
• ⚠️ File outside kits/bundles/templates modified: .github/workflows/validate-pr.yml

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🎉 All checks passed! This contribution follows the AgentKit structure.