Handle missing PR-head refs in centralized slash-command dispatch

[Copilot]

Centralized slash-command routing can fail for PR-originated events when the computed dispatch ref (PR head branch) is not available to workflow_dispatch in the target repo context. This change makes dispatch resilient by retrying on a safe default branch ref instead of aborting routing.

• Dispatch fallback for PR ref mismatches

  • In route_slash_command.cjs, dispatchWorkflow(...) now detects 422 errors with missing-ref semantics ("No ref found for").
  • When detected, it resolves a fallback branch ref and retries dispatch once with that ref.

• Fallback ref resolution

  • Added resolveDefaultBranchRef(ref) to derive fallback in priority order:
    1. context.payload.repository.default_branch
    2. repos.get(...).data.default_branch
    3. "main" as final fallback
  • Added small helpers to normalize and validate fallback refs so retries only occur when the fallback is usable and different from the failed ref.

• Error classification clarity

  • Added isMissingWorkflowDispatchRefError(error) to isolate ref-not-found failures from other 422 conditions (e.g., disabled workflow), preserving existing behavior for unrelated errors.

• Regression coverage

  • Added a focused test in route_slash_command.test.cjs for PR issue-comment routing:
    • first dispatch attempt fails on PR head ref not found,
    • second attempt retries on default branch and succeeds.

if (isMissingWorkflowDispatchRefError(error)) {
  const fallbackRef = await resolveDefaultBranchRef(ref);
  if (!fallbackRef) throw new Error(...);
  await github.rest.actions.createWorkflowDispatch({ workflow_id, ref: fallbackRef, inputs, headers });
}

[pelikhan]

@copilot the agentic commands dispatcher code is not properly capturing the pr Number

[github-actions]

🤖 PR Triage — §28282332784

Field	Value
Category	bug
Risk	medium
Score	53/100 (impact 30 + urgency 18 + quality 5)
Action	⏸ defer

Rationale: Draft PR with no CI yet. Slash-command dispatch resilience fix (164 additions, 2 files with tests) is meaningful but needs to leave draft status and pass CI before review.

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