Harden PR Sous Chef conclusion checkout to prevent MODULE_NOT_FOUND failure cascade

[Copilot]

A transient network/DNS failure during the conclusion job’s Checkout actions folder step was causing a second-order crash (MODULE_NOT_FOUND for setup_globals.cjs and related helpers), obscuring the real root cause. This change hardens that path so checkout failures are retried and, if still unsuccessful, fail with a direct checkout error instead of cascading module errors.

• Scope

  • Targets the pr-sous-chef conclusion setup path specifically (WorkflowID == "pr-sous-chef"), without changing checkout behavior for other workflows/jobs.

• Conclusion checkout resilience

  • Adds retry/backoff checkout generation for the conclusion setup path:
    • attempt 1
    • retry after 5s
    • retry after 15s
  • Each attempt is continue-on-error: true, followed by an explicit terminal step that emits a clear checkout failure message and exits non-zero if all attempts fail.

• Compiler and generated workflow updates

  • Adds generateCheckoutActionsFolderWithRetry(...) in the workflow compiler.
  • Wires conclusion setup (buildConclusionSetupSteps) to use retrying checkout for pr-sous-chef.
  • Regenerates .github/workflows/pr-sous-chef.lock.yml to include the retry sequence in the conclusion job.

• Regression guardrails

  • Adds focused compiler tests for:
    • retry-step generation shape/content
    • pr-sous-chef-only application of retrying checkout in conclusion setup.

- name: Checkout actions folder
  id: checkout-actions-folder-attempt-1
  continue-on-error: true
  uses: actions/checkout@...
  with:
    repository: github/gh-aw
    sparse-checkout: |
      actions

- name: Backoff before retrying checkout actions folder (5s)
  if: steps.checkout-actions-folder-attempt-1.outcome == 'failure'
  run: sleep 5

# ...attempt-2, backoff 15s, attempt-3...

- name: Fail with clear checkout error after retries
  if: steps.checkout-actions-folder-attempt-3.outcome == 'failure'
  run: |
    echo "::error::Failed to checkout github/gh-aw actions folder after 3 attempts (5s/15s backoff). This is usually a transient GitHub DNS or network failure."
    exit 1

• Fixes [aw-failures] Conclusion job's setup_globals.cjs MODULE_NOT_FOUND cascade has regressed (repeat of #28149) #49023