ENH: Optimize GitHub Actions ccache strategy with config-based keys

Improve the ccache caching strategy in pixi.yml and arm.yml:

- Key cache on OS + build config + build-system file hashes rather
  than github.sha. This gives reuse when source files change but
  the toolchain/build-config is still compatible, which is exactly
  where ccache pays off. ccache itself handles source-level reuse.
- Add tiered restore-keys fallback (OS+config → OS-only) so PR
  branches inherit the best available cache via GitHub's built-in
  branch scoping (PRs can read default branch caches)
- Save cache on all branches (if: always()), not just main, so
  PR branches benefit from incremental caches across pushes
- Bump cache key version to v3 to avoid restoring old caches
- Remove CCACHE_NODIRECT=1 to enable direct mode for better hit
  rates (CCACHE_COMPILERCHECK=content already ensures correctness)
- Increase CCACHE_MAXSIZE from 2.4G to 5G to leverage larger
  storage limits
- Use separate restore/save actions to support saving even on
  build failure (if: always())

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hjmjohnson

.github/workflows/arm.yml

@@ -94,9 +94,8 @@ jobs:
           echo "CCACHE_BASEDIR=${GITHUB_WORKSPACE}" >> "$GITHUB_ENV"
           echo "CCACHE_COMPILERCHECK=content" >> "$GITHUB_ENV"
           echo "CCACHE_NOHASHDIR=true" >> "$GITHUB_ENV"
-          echo "CCACHE_NODIRECT=1" >> "$GITHUB_ENV"
           echo "CCACHE_DIR=${{ runner.temp }}/ccache" >> "$GITHUB_ENV"
-          echo "CCACHE_MAXSIZE=2.4G" >> "$GITHUB_ENV"
+          echo "CCACHE_MAXSIZE=5G" >> "$GITHUB_ENV"
           if [ "$RUNNER_OS" == "Linux" ]; then
             sudo apt-get update -qq && sudo apt-get install -y ccache locales
             sudo locale-gen de_DE.UTF-8
@@ -109,7 +108,11 @@ jobs:
         uses: actions/cache/restore@v5
         with:
           path: ${{ runner.temp }}/ccache
-          key: ccache-v1-${{ matrix.os }}-${{ matrix.name }}
+          key: >-
+            ccache-v3-${{ runner.os }}-${{ matrix.name }}-${{ hashFiles('CMakeLists.txt', 'cmake/**', '**/*.cmake', '**/pyproject.toml', '**/pixi.lock') }}
+          restore-keys: |
+            ccache-v3-${{ runner.os }}-${{ matrix.name }}-
+            ccache-v3-${{ runner.os }}-
 
       - name: Show ccache configuration, stats and maintenance
         shell: bash
@@ -170,11 +173,12 @@ jobs:
         env:
           CTEST_OUTPUT_ON_FAILURE: 1
       - name: Save compiler cache
-        if: github.ref == 'refs/heads/main'
+        if: always()
         uses: actions/cache/save@v5
         with:
           path: ${{ runner.temp }}/ccache
-          key: ccache-v1-${{ matrix.os }}-${{ matrix.name }}
+          key: >-
+            ccache-v3-${{ runner.os }}-${{ matrix.name }}-${{ hashFiles('CMakeLists.txt', 'cmake/**', '**/*.cmake', '**/pyproject.toml', '**/pixi.lock') }}
 
       - name: ccache stats
         if: always()

.github/workflows/pixi.yml

@@ -53,9 +53,8 @@ jobs:
             echo "CCACHE_BASEDIR=${GITHUB_WORKSPACE}" >> "$GITHUB_ENV"
             echo "CCACHE_COMPILERCHECK=content" >> "$GITHUB_ENV"
             echo "CCACHE_NOHASHDIR=true" >> "$GITHUB_ENV"
-            echo "CCACHE_NODIRECT=1" >> "$GITHUB_ENV"
             echo "CCACHE_DIR=${{ runner.temp }}/ccache" >> "$GITHUB_ENV"
-            echo "CCACHE_MAXSIZE=2.4G" >> "$GITHUB_ENV"
+            echo "CCACHE_MAXSIZE=5G" >> "$GITHUB_ENV"
             if [ "$RUNNER_OS" == "Linux" ]; then
               sudo apt-get update -qq && sudo apt-get install -y ccache locales
               sudo locale-gen de_DE.UTF-8
@@ -70,7 +69,11 @@ jobs:
           uses: actions/cache/restore@v5
           with:
             path: ${{ runner.temp }}/ccache
-            key: ccache-v1-${{ matrix.os }}-pixi-cxx
+            key: >-
+              ccache-v3-${{ runner.os }}-pixi-cxx-${{ hashFiles('CMakeLists.txt', 'cmake/**', '**/*.cmake', '**/pyproject.toml', '**/pixi.lock') }}
+            restore-keys: |
+              ccache-v3-${{ runner.os }}-pixi-cxx-
+              ccache-v3-${{ runner.os }}-
 
         - name: Show ccache configuration, stats and maintenance
           shell: bash
@@ -150,11 +153,12 @@ jobs:
             echo "****** df -h /"
             df -h /
         - name: Save compiler cache
-          if: github.ref == 'refs/heads/main'
+          if: always()
           uses: actions/cache/save@v5
           with:
             path: ${{ runner.temp }}/ccache
-            key: ccache-v1-${{ matrix.os }}-pixi-cxx
+            key: >-
+              ccache-v3-${{ runner.os }}-pixi-cxx-${{ hashFiles('CMakeLists.txt', 'cmake/**', '**/*.cmake', '**/pyproject.toml', '**/pixi.lock') }}
 
         - name: ccache stats
           if: always()