MAINT Publish the backend log from the shared test jobs

The end-to-end tests launch pyrit_backend through ServerLauncher, which writes
the server log to a file in the system temp directory and then discards it when
the agent is torn down. A failing job therefore reports only the client side of
the failure, so a backend that is alive but unresponsive is indistinguishable
from one that never started.

Collect that log and publish it as a pipeline artifact, following the pattern
already used by adversarial-benchmark.yml. The collection step tolerates a
missing file so the jobs that do not launch a backend are unaffected, and the
publish step is skipped entirely when no log was found.

Author: varunj-msft

.azuredevops/test-job-template.yml

@@ -129,6 +129,39 @@ jobs:
         else
           make ${{ parameters.makeTarget }}
         fi
+  - bash: |
+      set -uo pipefail
+      artifact_dir="$(Build.ArtifactStagingDirectory)/backend-logs"
+      mkdir -p "$artifact_dir"
+
+      # ServerLauncher writes the backend log to tempfile.gettempdir(), which honours
+      # TMPDIR/TEMP/TMP before falling back to /tmp, so check the agent temp directory too.
+      for candidate in "${TMPDIR:-}" "${AGENT_TEMPDIRECTORY:-}" /tmp; do
+        [ -n "$candidate" ] || continue
+        if [ -f "$candidate/pyrit_backend.log" ]; then
+          # Only claim success, and only ask for a publish, if the copy actually landed;
+          # publishing an empty directory would report a log that isn't there.
+          if cp "$candidate/pyrit_backend.log" "$artifact_dir/pyrit_backend.log"; then
+            echo "Collected backend log from $candidate"
+            echo "##vso[task.setvariable variable=backendLogFound]true"
+          fi
+          break
+        fi
+      done
+
+      if [ ! -f "$artifact_dir/pyrit_backend.log" ]; then
+        echo "No pyrit_backend.log found; this job does not launch a backend."
+      fi
+    displayName: "Collect pyrit_backend log"
+    name: collect_backend_log
+    condition: always()
+  - task: PublishPipelineArtifact@1
+    displayName: "Publish pyrit_backend log"
+    condition: and(always(), eq(variables['backendLogFound'], 'true'))
+    inputs:
+      targetPath: $(Build.ArtifactStagingDirectory)/backend-logs
+      artifactName: backend-logs-${{ parameters.jobName }}-$(Build.BuildId)
+      publishLocation: pipeline
   - bash: |
       rm -f ~/.pyrit/.env ~/.pyrit/.env.local
     name: clean_up_env_files