diff --git a/.gitea/workflows/runner-probe.yml b/.gitea/workflows/runner-probe.yml
new file mode 100644
index 0000000..10973fb
--- /dev/null
+++ b/.gitea/workflows/runner-probe.yml
@@ -0,0 +1,80 @@
+name: runner-probe
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - ".gitea/workflows/runner-probe.yml"
+  workflow_dispatch:
+
+jobs:
+  probe:
+    runs-on: gitea-cicd-server-for-CODEX
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Identify the runner
+        run: |
+          set -eu
+          echo "runner=${RUNNER_NAME:-unknown}"
+          echo "labels=${RUNNER_LABELS:-unknown}"
+          uname -a
+          id
+          df -h /
+
+      - name: Check Docker and the persistent service
+        run: |
+          set -eu
+          if ! command -v docker >/dev/null 2>&1; then
+            echo "docker=missing"
+            exit 0
+          fi
+          docker version --format 'client {{.Client.Version}} / server {{.Server.Version}}'
+          docker ps -a --format 'container={{.Names}} status={{.Status}} image={{.Image}}'
+          docker volume ls --format 'volume={{.Name}}'
+
+      - name: Find the uploaded Iowa algebra PDF
+        run: |
+          set -eu
+          target=uiowa-algebra.pdf
+          found=0
+
+          for root in "$GITHUB_WORKSPACE" /books /data /srv /opt /workspace; do
+            if [ -d "$root" ]; then
+              while IFS= read -r path; do
+                [ -n "$path" ] || continue
+                found=1
+                echo "FOUND host:$path"
+                stat -c 'size=%s bytes modified=%y' "$path" 2>/dev/null || ls -lh "$path"
+                sha256sum "$path" 2>/dev/null || true
+              done <<EOF
+          $(find "$root" -maxdepth 5 -type f -name "$target" 2>/dev/null || true)
+          EOF
+            fi
+          done
+
+          if command -v docker >/dev/null 2>&1; then
+            if docker ps -a --format '{{.Names}}' | grep -qx lean-bench; then
+              if docker exec lean-bench test -f "/books/$target"; then
+                found=1
+                echo "FOUND container:lean-bench:/books/$target"
+                docker exec lean-bench sh -c "ls -lh '/books/$target'; sha256sum '/books/$target'"
+              fi
+            fi
+
+            if docker volume inspect lean-bench-books >/dev/null 2>&1; then
+              mountpoint="$(docker volume inspect lean-bench-books --format '{{.Mountpoint}}')"
+              if [ -f "$mountpoint/$target" ]; then
+                found=1
+                echo "FOUND volume:lean-bench-books:$target"
+                ls -lh "$mountpoint/$target"
+                sha256sum "$mountpoint/$target" 2>/dev/null || true
+              fi
+            fi
+          fi
+
+          if [ "$found" -eq 0 ]; then
+            echo "NOT_FOUND: $target"
+            exit 2
+          fi