Add Docker build and cache cleanup steps in CI, prevent redundant builds in Swarm E2E tests

- Updated GitHub workflow to include Docker cache cleanup and image build steps.
- Modified Swarm E2E test logic to skip Docker image build if it already exists, optimizing CI performance.

.github/workflows/build.yml

@@ -148,6 +148,14 @@ jobs:
           export PATH="$HOME/.local/bin:$PATH"
           uv sync --group dev
 
+      - name: Clean Docker build cache
+        run: docker builder prune -af
+
+      - name: Build Docker image
+        env:
+          DOCKER_BUILDKIT: "0"
+        run: docker build -t byjg/easy-haproxy:local -f deploy/docker/Dockerfile .
+
       - name: Run Swarm E2E tests
         run: |
           export PATH="$HOME/.local/bin:$PATH"

tests_e2e/test_swarm.py

@@ -60,14 +60,25 @@ _cloudflare_config_created = False
 def ensure_haproxy_image():
     """Build byjg/easy-haproxy:local from source at the start of the test session.
 
-    Always builds on the first call so tests run against the current codebase,
+    If the image already exists (e.g. pre-built by a CI step), the build is
-    never a stale image left over from a previous session or docker compose run.
+    skipped so that CI can control how/when the image is built without the
+    pytest session re-triggering a potentially slow or hanging `docker build`.
     Subsequent calls within the same session are no-ops (image already built).
     """
     global _swarm_image_built
     if _swarm_image_built:
         return
 
+    # Skip build if image already exists (e.g. pre-built in CI)
+    inspect = subprocess.run(
+        ["docker", "image", "inspect", "byjg/easy-haproxy:local"],
+        capture_output=True,
+    )
+    if inspect.returncode == 0:
+        print("\n  ✓ byjg/easy-haproxy:local already exists, skipping build")
+        _swarm_image_built = True
+        return
+
     project_root = BASE_DIR.parent
     print("\n  → Building byjg/easy-haproxy:local from source...")
     subprocess.run(