Fallback build warmup binary during deploy (#6946)

.github/workflows/docker_build.yml

@@ -299,11 +299,25 @@ jobs:
           ssh-keyscan -H "$DO_DROPLET_IP" >> ~/.ssh/known_hosts 2>/dev/null || true
 
       - name: Download warmup binary
+        id: download-warmup
+        continue-on-error: true
         uses: actions/download-artifact@v8
         with:
           name: warmup-binary
           path: scripts/bin/
 
+      - name: Build warmup binary fallback
+        if: steps.download-warmup.outcome != 'success'
+        run: |
+          echo "::warning::warmup-binary artifact was unavailable; rebuilding warmup binary before deploy"
+          ./ci/github_actions/ensure_bazel_installed.sh
+          bazel build \
+            --platforms=//:linux_x86_64 \
+            --extra_toolchains=@llvm_toolchain_linux//:all \
+            //ci:warmup_tar
+          mkdir -p scripts/bin
+          tar -xf bazel-bin/ci/warmup_tar.tar -C scripts/bin --strip-components=1
+
       - name: Copy config files to droplet
         run: |
           # Create directory structure on remote