ci(e2e): switch FUSE Mount build to Azure Ubuntu mirror, persist buildx cache

archive.ubuntu.com from GitHub-hosted runners has been Ign:/retrying for
~60s per package, eating the Start SeaweedFS step's 10-min budget before
apt-get install finishes. The host already uses azure.archive.ubuntu.com;
do the same inside Dockerfile.e2e and drop the Retries=5 amplifier.

Also rotate /tmp/.buildx-cache-new over /tmp/.buildx-cache so the apt
layer actually survives across runs, and bump the step to 15 minutes
as a safety margin.

.github/workflows/e2e.yml

@@ -57,12 +57,12 @@ jobs:
         echo "FUSE device: $(ls -la /dev/fuse 2>&1 || echo '/dev/fuse not found')"
 
     - name: Start SeaweedFS
-      timeout-minutes: 10
+      timeout-minutes: 15
       run: |
         # Enable Docker buildkit for better caching
         export DOCKER_BUILDKIT=1
         export COMPOSE_DOCKER_CLI_BUILD=1
-        
+
         # Build with retry logic
         for i in {1..3}; do
           echo "Build attempt $i/3"
@@ -77,10 +77,18 @@ jobs:
             sleep 30
           fi
         done
-        
+
         # Start services with wait
         docker compose -f ./compose/e2e-mount.yml up --wait
 
+    - name: Rotate buildx cache
+      if: always()
+      run: |
+        # Without this, --cache-to writes to .buildx-cache-new but actions/cache only
+        # uploads .buildx-cache, so layers (notably the slow apt RUN) never persist.
+        rm -rf /tmp/.buildx-cache
+        if [ -d /tmp/.buildx-cache-new ]; then mv /tmp/.buildx-cache-new /tmp/.buildx-cache; fi
+
     - name: Run FIO 4k
       timeout-minutes: 15
       run: |

docker/Dockerfile.e2e

@@ -2,13 +2,15 @@ FROM ubuntu:22.04
 
 LABEL author="Chris Lu"
 
-# Use faster mirrors and optimize package installation
+# Use Azure's Ubuntu mirror — much faster than archive.ubuntu.com from GitHub-hosted runners,
+# which have been hanging long enough on Ign:/retry to trip the 10-min step timeout.
 # Note: This e2e test image intentionally runs as root for simplicity and compatibility.
 # Production images (Dockerfile.go_build) use proper user isolation with su-exec.
 # For testing purposes, running as root avoids permission complexities and dependency
 # on Alpine-specific tools like su-exec (not available in Ubuntu repos).
-RUN apt-get -o Acquire::Retries=5 -o Acquire::http::Timeout=30 update && \
-    DEBIAN_FRONTEND=noninteractive apt-get -o Acquire::Retries=5 -o Acquire::http::Timeout=30 install -y \
+RUN sed -i 's|http://archive.ubuntu.com/ubuntu|http://azure.archive.ubuntu.com/ubuntu|g; s|http://security.ubuntu.com/ubuntu|http://azure.archive.ubuntu.com/ubuntu|g' /etc/apt/sources.list && \
+    apt-get -o Acquire::http::Timeout=15 update && \
+    DEBIAN_FRONTEND=noninteractive apt-get -o Acquire::http::Timeout=15 install -y \
     --no-install-recommends \
     --no-install-suggests \
     curl \