feat(ci): Add test failure reporting with PR comments and error annotations

When tests fail in CI, capture the failed test names from ctest output
and surface them in two ways:
- GitHub Actions ::error:: annotations visible in the job summary
- Automatic PR comment listing the specific failed tests with a link
  to the full logs

Applied to both Linux adapters release and Ubuntu debug test jobs.

Author: kgpai

.github/workflows/linux-build-base.yml

@@ -96,6 +96,7 @@ jobs:
       cudf-changes: ${{ steps.changes.outputs.cudf }}
       build-outcome: ${{ steps.build.outcome }}
       test-outcome: ${{ steps.tests.outcome }}
+      failed-tests: ${{ steps.tests.outputs.failed-tests }}
     steps:
       - uses: actions/checkout@v5
         with:
@@ -196,7 +197,22 @@ jobs:
         run: |
           source /setup-classpath.sh
           ulimit -n 65536
-          ctest -j 24 --timeout 900 --label-exclude cuda_driver --output-on-failure --no-tests=error
+          set +e
+          ctest -j 24 --timeout 900 --label-exclude cuda_driver --output-on-failure --no-tests=error 2>&1 | tee /tmp/ctest-output.log
+          CTEST_EXIT=${PIPESTATUS[0]}
+          set -e
+          if [[ $CTEST_EXIT -ne 0 ]]; then
+            FAILED_TESTS=$(grep -A 1000 'The following tests FAILED:' /tmp/ctest-output.log | grep -E '^\s+[0-9]+ - ' | sed 's/.*- \(.*\) (.*/\1/' || true)
+            if [[ -n "$FAILED_TESTS" ]]; then
+              echo "::error::Failed tests in Linux adapters release: $(echo "$FAILED_TESTS" | tr '\n' ', ' | sed 's/, $//')"
+              {
+                echo 'failed-tests<<EOF'
+                echo "$FAILED_TESTS"
+                echo 'EOF'
+              } >> "$GITHUB_OUTPUT"
+            fi
+            exit 1
+          fi
 
       # Clang-tidy needs a complete build because some files are only generated during the build
       # that clang tidy will not find and report errors otherwise.
@@ -315,13 +331,44 @@ jobs:
             exit 1
           fi
           if [[ "$TEST_OUTCOME" != "success" ]]; then
+            if [[ -n "$FAILED_TESTS" ]]; then
+              echo "::error::The following tests failed in Linux adapters release:"
+              echo "$FAILED_TESTS" | while read -r test; do
+                echo "::error::  - $test"
+              done
+            fi
             echo "Tests failed."
             exit 1
           fi
           echo "Tests passed."
         env:
           BUILD_OUTCOME: ${{ needs.adapters.outputs.build-outcome }}
           TEST_OUTCOME: ${{ needs.adapters.outputs.test-outcome }}
+          FAILED_TESTS: ${{ needs.adapters.outputs.failed-tests }}
+
+      - name: Comment on PR with test failures
+        if: failure() && needs.adapters.outputs.failed-tests != ''
+        env:
+          GH_TOKEN: ${{ github.token }}
+          FAILED_TESTS: ${{ needs.adapters.outputs.failed-tests }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+        run: |
+          PR_NUMBER="${{ github.event.pull_request.number }}"
+          if [[ -z "$PR_NUMBER" ]]; then
+            echo "Not a pull request — skipping comment."
+            exit 0
+          fi
+          FORMATTED=$(echo "$FAILED_TESTS" | sed 's/^/- /')
+          BODY="### :x: Test Failures: Linux adapters release
+
+          The following tests failed:
+
+          ${FORMATTED}
+
+          :link: [View full test logs](${RUN_URL})"
+          gh pr comment "$PR_NUMBER" \
+            --repo "${{ github.repository }}" \
+            --body "$BODY"
 
   cudf-tests:
     runs-on: 4-core-ubuntu-gpu-t4
@@ -396,6 +443,7 @@ jobs:
     outputs:
       build-outcome: ${{ steps.build.outcome }}
       test-outcome: ${{ steps.tests.outcome }}
+      failed-tests: ${{ steps.tests.outputs.failed-tests }}
     defaults:
       run:
         shell: bash
@@ -493,7 +541,23 @@ jobs:
         if: steps.build.outcome == 'success'
         run: |
           ulimit -n 65536
-          cd _build/debug && ctest -j 24 --timeout 1800 --output-on-failure --no-tests=error
+          cd _build/debug
+          set +e
+          ctest -j 24 --timeout 1800 --output-on-failure --no-tests=error 2>&1 | tee /tmp/ctest-output.log
+          CTEST_EXIT=${PIPESTATUS[0]}
+          set -e
+          if [[ $CTEST_EXIT -ne 0 ]]; then
+            FAILED_TESTS=$(grep -A 1000 'The following tests FAILED:' /tmp/ctest-output.log | grep -E '^\s+[0-9]+ - ' | sed 's/.*- \(.*\) (.*/\1/' || true)
+            if [[ -n "$FAILED_TESTS" ]]; then
+              echo "::error::Failed tests in Ubuntu debug: $(echo "$FAILED_TESTS" | tr '\n' ', ' | sed 's/, $//')"
+              {
+                echo 'failed-tests<<EOF'
+                echo "$FAILED_TESTS"
+                echo 'EOF'
+              } >> "$GITHUB_OUTPUT"
+            fi
+            exit 1
+          fi
 
   ubuntu-debug-build-status:
     if: always()
@@ -522,13 +586,44 @@ jobs:
             exit 1
           fi
           if [[ "$TEST_OUTCOME" != "success" ]]; then
+            if [[ -n "$FAILED_TESTS" ]]; then
+              echo "::error::The following tests failed in Ubuntu debug:"
+              echo "$FAILED_TESTS" | while read -r test; do
+                echo "::error::  - $test"
+              done
+            fi
             echo "Tests failed."
             exit 1
           fi
           echo "Tests passed."
         env:
           BUILD_OUTCOME: ${{ needs.ubuntu-debug.outputs.build-outcome }}
           TEST_OUTCOME: ${{ needs.ubuntu-debug.outputs.test-outcome }}
+          FAILED_TESTS: ${{ needs.ubuntu-debug.outputs.failed-tests }}
+
+      - name: Comment on PR with test failures
+        if: failure() && needs.ubuntu-debug.outputs.failed-tests != ''
+        env:
+          GH_TOKEN: ${{ github.token }}
+          FAILED_TESTS: ${{ needs.ubuntu-debug.outputs.failed-tests }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+        run: |
+          PR_NUMBER="${{ github.event.pull_request.number }}"
+          if [[ -z "$PR_NUMBER" ]]; then
+            echo "Not a pull request — skipping comment."
+            exit 0
+          fi
+          FORMATTED=$(echo "$FAILED_TESTS" | sed 's/^/- /')
+          BODY="### :x: Test Failures: Ubuntu debug
+
+          The following tests failed:
+
+          ${FORMATTED}
+
+          :link: [View full test logs](${RUN_URL})"
+          gh pr comment "$PR_NUMBER" \
+            --repo "${{ github.repository }}" \
+            --body "$BODY"
 
   fedora-debug:
     runs-on: 32-core-ubuntu