fix(ci): make Warp ABBA evidence bounded and complete (#6417)

.github/workflows/performance-ab.yml

@@ -121,14 +121,14 @@ jobs:
           candidate_sha="$(git rev-parse HEAD)"
           if [[ "${{ github.event_name }}" == "schedule" ]]; then
             baseline_sha="${SCHEDULED_BASELINE_SHA:-$candidate_sha}"
-            if ! git merge-base --is-ancestor "$baseline_sha" "$candidate_sha"; then
-              echo "::error::scheduled baseline $baseline_sha is not an ancestor of candidate $candidate_sha" >&2
-              exit 1
-            fi
           else
             baseline_sha="$(git rev-parse origin/main)"
           fi
           git cat-file -e "${baseline_sha}^{commit}"
+          if ! git merge-base --is-ancestor "$baseline_sha" "$candidate_sha"; then
+            echo "::error::baseline $baseline_sha is not an ancestor of candidate $candidate_sha; update the selected ref before comparing" >&2
+            exit 1
+          fi
           echo "baseline_sha=$baseline_sha" >> "$GITHUB_OUTPUT"
           echo "candidate_sha=$candidate_sha" >> "$GITHUB_OUTPUT"
           echo "baseline commit: $baseline_sha"
@@ -342,6 +342,10 @@ jobs:
         if: always()
         run: |
           status="${{ steps.ab.outputs.status }}"
+          if [[ -z "$status" ]]; then
+            echo "::error::warp A/B setup failed before the rig ran. Check the first failed workflow step." >&2
+            exit 1
+          fi
           if [[ "$status" != "0" ]]; then
             echo "::error::warp A/B budget gate failed (exit $status). See the step summary / gate.md artifact." >&2
             exit "$status"