ci: use Warp cache for Docker layers

Speeds of 1MB/s and 15 minute cached docker image pulls during builds
are not uncommon.

Warp runners provide a local GitHub Actions cache protocol proxy for
Docker layer cache traffic. Point BuildKit's gha cache backend at that
proxy on Warp runners so cached image layers do not have to be fetched
from GitHub's slower cache service.

Add a default for provider so other users (e.g. qa-assets) don't have to
update this unless they use custome runners.

.github/actions/configure-docker/action.yml

@@ -1,9 +1,22 @@
 name: 'Configure Docker'
 description: 'Set up Docker build driver and configure build cache args'
+inputs:
+  provider:
+    description: 'The cache provider to use'
+    required: false
+    default: 'gha'
 runs:
   using: 'composite'
   steps:
+    - name: Set up Docker Buildx for Warp cache
+      if: ${{ inputs.provider == 'warp' }}
+      uses: docker/setup-buildx-action@v4
+      with:
+        driver-opts: |
+          network=host
+
     - name: Set up Docker Buildx
+      if: ${{ inputs.provider != 'warp' }}
       uses: docker/setup-buildx-action@v4
 
     # This is required when using the gha cache backend with a manual docker buildx invocation.
@@ -23,13 +36,18 @@ runs:
     - name: Construct docker build cache args
       shell: bash
       run: |
+        cache_options="scope=${CONTAINER_NAME}"
+        if [[ "${{ inputs.provider }}" == "warp" ]]; then
+          cache_options="url=http://127.0.0.1:49160/,version=1,${cache_options}"
+        fi
+
         # Configure docker build cache backend
         # Always optimistically --cache‑from in case a cache blob exists
-        args=(--cache-from "type=gha,scope=${CONTAINER_NAME}")
+        args=(--cache-from "type=gha,${cache_options}")
 
         # Only add --cache-to when pushing to the default branch.
         if [[ ${{ github.event_name }} == "push" && ${{ github.ref_name }} == ${{ github.event.repository.default_branch }} ]]; then
-          args+=(--cache-to "type=gha,mode=max,ignore-error=true,scope=${CONTAINER_NAME}")
+          args+=(--cache-to "type=gha,mode=max,ignore-error=true,${cache_options}")
         fi
 
         # Always `--load` into docker images (needed when using the `docker-container` build driver).

.github/workflows/ci.yml

@@ -363,6 +363,8 @@ jobs:
 
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
+        with:
+          provider: ${{ needs.runners.outputs.provider }}
 
       - name: CI script
         run: ./ci/test_run_all.sh
@@ -557,6 +559,8 @@ jobs:
 
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
+        with:
+          provider: ${{ matrix.provider || needs.runners.outputs.provider }}
 
       - name: Clear unnecessary files
         if: ${{ needs.runners.outputs.provider == 'gha' && true || false }} # Only needed on GHA runners
@@ -600,6 +604,8 @@ jobs:
 
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
+        with:
+          provider: ${{ needs.runners.outputs.provider }}
 
       - name: CI script
         run: |