fix: remove sandbox image cache that adds ~4.5 min overhead per run

The sandbox image cache never provides a net time savings. The cache key
is based on the image name (not its digest), so the cached tar is always
stale. Every run pays the full cycle: restore, load, pull, save, upload
(~4.5 min) when a bare pull takes ~30s.

Remove the cache/restore, load, save, and cache/save steps entirely.
Drop skopeo (only used for digest comparison in the cache logic).
Simplify the pre-pull step to a straight podman pull.

Closes #2222

Signed-off-by: Ralph Bean <rbean@redhat.com>
Assisted-by: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Ralph Bean <rbean@redhat.com>

Author: ralphbean

action.yml

@@ -253,7 +253,7 @@ runs:
       shell: bash
       run: |
         sudo apt-get update
-        sudo apt-get install -y podman skopeo
+        sudo apt-get install -y podman
         podman --version
 
     - name: Configure rootless Podman
@@ -286,66 +286,12 @@ runs:
       shell: bash
       run: "$GITHUB_ACTION_PATH/.github/scripts/install-openshell.sh"
 
-    - name: Restore cached sandbox image
-      id: sandbox-cache
-      uses: actions/cache/restore@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
-      with:
-        path: /tmp/sandbox-image.tar
-        key: sandbox-image-${{ runner.os }}-${{ runner.arch }}-${{ env.FULLSEND_SANDBOX_IMAGE || 'ghcr.io/fullsend-ai/fullsend-code:latest' }}
-        restore-keys: |
-          sandbox-image-${{ runner.os }}-${{ runner.arch }}-
-
-    - name: Load cached sandbox image
-      if: steps.sandbox-cache.outputs.cache-hit == 'true'
-      shell: bash
-      run: podman load -i /tmp/sandbox-image.tar || echo "::warning::Cached image load failed; will pull fresh"
-
     - name: Pre-pull sandbox image
-      id: sandbox-pull
       shell: bash
       run: |
         IMAGE="${FULLSEND_SANDBOX_IMAGE:-ghcr.io/fullsend-ai/fullsend-code:latest}"
         echo "Pre-pulling sandbox image: ${IMAGE}"
-
-        LOCAL_DIGEST="$(podman image inspect --format '{{.Digest}}' -- "${IMAGE}" 2>/dev/null || true)"
-
-        if [[ -n "${LOCAL_DIGEST}" ]]; then
-          # Check remote digest without pulling (~1s HEAD request).
-          REMOTE_DIGEST="$(skopeo inspect --no-tags --format '{{.Digest}}' "docker://${IMAGE}" 2>/dev/null || true)"
-          if [[ -z "${REMOTE_DIGEST}" ]]; then
-            echo "Could not fetch remote digest; falling through to pull"
-          elif [[ "${LOCAL_DIGEST}" == "${REMOTE_DIGEST}" ]]; then
-            echo "Local image is current (digest ${LOCAL_DIGEST:0:19}…); skipping pull"
-            exit 0
-          else
-            echo "Digest mismatch (local=${LOCAL_DIGEST:0:19}… remote=${REMOTE_DIGEST:0:19}…); pulling"
-          fi
-        fi
-
         timeout 300 podman pull -- "${IMAGE}" || echo "::warning::Image pre-pull failed; sandbox create will pull on demand"
-        PULLED_DIGEST="$(podman image inspect --format '{{.Digest}}' -- "${IMAGE}" 2>/dev/null || true)"
-        if [[ "${LOCAL_DIGEST}" != "${PULLED_DIGEST}" ]]; then
-          echo "changed=true" >> "${GITHUB_OUTPUT}"
-        fi
-
-    - name: Save sandbox image for cache
-      if: steps.sandbox-cache.outputs.cache-hit != 'true' || steps.sandbox-pull.outputs.changed == 'true'
-      shell: bash
-      run: |
-        IMAGE="${FULLSEND_SANDBOX_IMAGE:-ghcr.io/fullsend-ai/fullsend-code:latest}"
-        if podman image exists -- "${IMAGE}"; then
-          rm -f /tmp/sandbox-image.tar
-          podman save -o /tmp/sandbox-image.tar -- "${IMAGE}"
-        else
-          echo "::warning::Image not available to cache"
-        fi
-
-    - name: Update sandbox image cache
-      if: steps.sandbox-cache.outputs.cache-hit != 'true' || steps.sandbox-pull.outputs.changed == 'true'
-      uses: actions/cache/save@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
-      with:
-        path: /tmp/sandbox-image.tar
-        key: sandbox-image-${{ runner.os }}-${{ runner.arch }}-${{ env.FULLSEND_SANDBOX_IMAGE || 'ghcr.io/fullsend-ai/fullsend-code:latest' }}
 
     - name: Install validation dependencies
       shell: bash