[CI] Stop caching what the cache inventory says is not being used

.github/workflows/codeql.yml

@@ -51,6 +51,11 @@ jobs:
         # https://docs.github.com/en/code-security/reference/code-scanning/codeql/codeql-queries/actions-built-in-queries
         queries: security-extended
         dependency-caching: true
+        # A TRAP cache costs about 974 MiB per language here. On master that is worth
+        # paying, because the next push reuses it. On a pull request it is pure loss:
+        # the cache lands on refs/pull/N/merge, which no other run ever reads, so every
+        # new pull request leaves a dead 974 MiB entry behind.
+        trap-caching: ${{ github.event_name != 'pull_request' }}
 
     - name: "[C++] Install dependencies"
       if: matrix.language == 'cpp' && matrix.build-mode == 'manual'

.github/workflows/desktop-build.yml

@@ -176,7 +176,7 @@ jobs:
     continue-on-error: ${{ matrix.allow-failure == 'yes' }}
     timeout-minutes: 70
     env:
-      CACHE: ${{ github.workspace }}/.cache/${{ matrix.distro }}${{ matrix.version }}${{ matrix.variant }}    # directory for caching docker image and ccache
+      CACHE: ${{ github.workspace }}/.cache/${{ matrix.distro }}${{ matrix.version }}${{ matrix.variant }}    # directory holding the build image and ccache, only the image subdir is cached below
       CCACHE_EVICTION_AGE: 7d
       CCACHE_SIZE: 600M    # space of all repo is 10Gi: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#usage-limits-and-eviction-policy
       CMAKE_GENERATOR: 'Ninja'
@@ -187,12 +187,18 @@ jobs:
       - name: "Checkout"
         uses: actions/checkout@v7
 
-      - name: "Restore compiler cache (ccache)"
+      # Only the image half of this cache is worth keeping. A compile on these legs runs
-        id: restore_ccache
+      # inside a container, so ccache measures a 0.00 to 1.85 percent hit rate here against
+      # 49 to 50 percent on the macOS legs, and the roughly 420 MiB of ccache each entry
+      # carried was buying nothing. Caching $CACHE/image alone drops that.
+      # The key changes name because the cached content does: the old ccache-<distro>
+      # entries hold an image plus a ccache directory, and expire on their own untouched.
+      - name: "Restore build image cache"
+        id: restore_image_cache
         uses: actions/cache/restore@v6
         with:
-          key: ccache-${{ matrix.distro }}${{ matrix.version }}${{ matrix.variant }}
+          key: image-${{ matrix.distro }}${{ matrix.version }}${{ matrix.variant }}
-          path: ${{ env.CACHE }}/.ccache
+          path: ${{ env.CACHE }}/image
 
       - name: "Build ${{ matrix.distro }} ${{ matrix.version }} Docker image"
         shell: bash
@@ -313,24 +319,24 @@ jobs:
           # comes from the client event itself (COCKATRICE_SENTRY_RELEASE).
           sentry-cli debug-files upload --org cockatrice --project cockatrice-desktop "${paths[@]}"
 
-      # Delete used cache to emulate a ccache update. See https://github.com/actions/cache/issues/342
+      # Delete used cache to emulate a cache update. See https://github.com/actions/cache/issues/342
-      - name: "Delete remote compiler cache (ccache)"
+      - name: "[Linux] Delete used cache to emulate a cache update"
-        if: github.ref == 'refs/heads/master' && steps.restore_ccache.outputs.cache-hit
+        if: github.ref == 'refs/heads/master' && steps.restore_image_cache.outputs.cache-hit
         continue-on-error: true
         env:
-          CACHE_PRIMARY_KEY: ${{ steps.restore_ccache.outputs.cache-primary-key }}
+          CACHE_PRIMARY_KEY: ${{ steps.restore_image_cache.outputs.cache-primary-key }}
           GH_TOKEN: ${{ github.token }}
         run: |
           if gh cache delete --repo "$GITHUB_REPOSITORY" "$CACHE_PRIMARY_KEY"; then
             echo "Cache deleted successfully"
           fi
 
-      - name: "Save updated compiler cache (ccache)"
+      - name: "Save updated build image cache"
         if: github.ref == 'refs/heads/master'
         uses: actions/cache/save@v6
         with:
-          key: ${{ steps.restore_ccache.outputs.cache-primary-key }}
+          key: ${{ steps.restore_image_cache.outputs.cache-primary-key }}
-          path: ${{ env.CACHE }}/.ccache
+          path: ${{ env.CACHE }}/image
 
       - name: "Upload artifact"
         id: upload_artifact
@@ -491,7 +497,7 @@ jobs:
 
       - name: "[macOS] Restore compiler cache (ccache)"
         if: matrix.os == 'macOS' && matrix.use_ccache == 1
-        id: restore_ccache
+        id: restore_image_cache
         uses: actions/cache/restore@v6
         with:
           key: ccache-${{ matrix.runner }}_${{ matrix.override_target }}-Xcode${{ matrix.xcode }}
@@ -815,10 +821,10 @@ jobs:
 
       # Delete used cache to emulate a ccache update. See https://github.com/actions/cache/issues/342
       - name: "[macOS] Delete remote compiler cache (ccache)"
-        if: matrix.os == 'macOS' && matrix.use_ccache == 1 && github.ref == 'refs/heads/master' && steps.restore_ccache.outputs.cache-hit
+        if: matrix.os == 'macOS' && matrix.use_ccache == 1 && github.ref == 'refs/heads/master' && steps.restore_image_cache.outputs.cache-hit
         continue-on-error: true
         env:
-          CACHE_PRIMARY_KEY: ${{ steps.restore_ccache.outputs.cache-primary-key }}
+          CACHE_PRIMARY_KEY: ${{ steps.restore_image_cache.outputs.cache-primary-key }}
           GH_TOKEN: ${{ github.token }}
         run: |
           if gh cache delete --repo "$GITHUB_REPOSITORY" "$CACHE_PRIMARY_KEY"; then
@@ -829,7 +835,7 @@ jobs:
         if: matrix.os == 'macOS' && matrix.use_ccache == 1 && github.ref == 'refs/heads/master'
         uses: actions/cache/save@v6
         with:
-          key: ${{ steps.restore_ccache.outputs.cache-primary-key }}
+          key: ${{ steps.restore_image_cache.outputs.cache-primary-key }}
           path: ${{ env.CCACHE_DIR }}
 
       - name: "[macOS] Sign app bundle"

.github/workflows/docker-release.yml

@@ -89,7 +89,10 @@ jobs:
         uses: docker/build-push-action@v7
         with:
           cache-from: type=gha,scope=${{ env.CACHE_SCOPE }}
-          cache-to: ${{ case(github.ref == 'refs/heads/master', format('type=gha,mode=max,scope={0}', env.CACHE_SCOPE), '') }}
+          # mode=min exports only the layers of the final image. mode=max also exports
+          # every intermediate build layer, which for this multi-stage build is where the
+          # bulk of the 42 cached blobs came from, and none of it survives into the image.
+          cache-to: ${{ case(github.ref == 'refs/heads/master', format('type=gha,mode=min,scope={0}', env.CACHE_SCOPE), '') }}
           context: .
           platforms: ${{ matrix.platform }}
           push: false
@@ -101,7 +104,7 @@ jobs:
         uses: docker/build-push-action@v7
         with:
           cache-from: type=gha,scope=${{ env.CACHE_SCOPE }}
-          cache-to: type=gha,mode=max,scope=${{ env.CACHE_SCOPE }}
+          cache-to: type=gha,mode=min,scope=${{ env.CACHE_SCOPE }}
           context: .
           labels: |
             org.opencontainers.image.description=${{ env.OCI_DESCRIPTION }}