docker: base and sdk images

Author: stephen-derosa

.github/workflows/builds.yml

@@ -14,7 +14,8 @@ on:
       - build.cmd
       - vcpkg.json
       - CMakePresets.json
-      - docker/Dockerfile
+      - docker/Dockerfile.base
+      - docker/Dockerfile.sdk
       - .github/workflows/**
   pull_request:
     branches: ["main"]
@@ -29,7 +30,8 @@ on:
       - build.cmd
       - vcpkg.json
       - CMakePresets.json
-      - docker/Dockerfile
+      - docker/Dockerfile.base
+      - docker/Dockerfile.sdk
       - .github/workflows/**
   workflow_dispatch:
 
@@ -332,6 +334,7 @@ jobs:
   docker-build-x64:
     name: Build (docker-linux-x64)
     runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
 
     steps:
       - name: Checkout (with submodules)
@@ -351,17 +354,21 @@ jobs:
           docker-images: true
           swap-storage: true
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3.11.1
+      - name: Build base Docker image
+        run: |
+          docker build \
+            --build-arg TARGETARCH=amd64 \
+            -t livekit-cpp-sdk-base-x64:${{ github.sha }} \
+            -f docker/Dockerfile.base \
+            docker
 
-      - name: Build Docker image
+      - name: Build SDK Docker image
         run: |
-          docker buildx build \
-            --platform linux/amd64 \
-            --load \
+          docker build \
+            --build-arg BASE_IMAGE=livekit-cpp-sdk-base-x64:${{ github.sha }} \
             -t livekit-cpp-sdk-x64:${{ github.sha }} \
             . \
-            -f docker/Dockerfile
+            -f docker/Dockerfile.sdk
 
       - name: Verify installed SDK inside image
         run: |
@@ -382,6 +389,7 @@ jobs:
   docker-build-linux-arm64:
     name: Build (docker-linux-arm64)
     runs-on: ubuntu-24.04-arm
+    if: github.event_name == 'pull_request'
 
     steps:
       - name: Checkout (with submodules)
@@ -401,17 +409,21 @@ jobs:
           docker-images: true
           swap-storage: true
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3.11.1
+      - name: Build base Docker image
+        run: |
+          docker build \
+            --build-arg TARGETARCH=arm64 \
+            -t livekit-cpp-sdk-base-arm64:${{ github.sha }} \
+            -f docker/Dockerfile.base \
+            docker
 
-      - name: Build Docker image
+      - name: Build SDK Docker image
         run: |
-          docker buildx build \
-            --platform linux/arm64 \
-            --load \
+          docker build \
+            --build-arg BASE_IMAGE=livekit-cpp-sdk-base-arm64:${{ github.sha }} \
             -t livekit-cpp-sdk:${{ github.sha }} \
             . \
-            -f docker/Dockerfile
+            -f docker/Dockerfile.sdk
 
       - name: Verify installed SDK inside image
         run: |
@@ -433,6 +445,7 @@ jobs:
     name: Build (cpp-example-collection-linux-arm64)
     runs-on: ubuntu-24.04-arm
     needs: docker-build-linux-arm64
+    if: github.event_name == 'pull_request'
 
     steps:
       - name: Download Docker image artifact
@@ -459,6 +472,7 @@ jobs:
     name: Build (cpp-example-collection-x64)
     runs-on: ubuntu-latest
     needs: docker-build-x64
+    if: github.event_name == 'pull_request'
 
     steps:
       - name: Download Docker image artifact