ci: add ccache persistence via actions/cache for build and release workflows

- Move CCACHE_DIR inside workspace for actions/cache compatibility
- Add CCACHE_BASEDIR for portable cache entries across workspaces
- Add cache restore step with fallback keys (branch -> main)
- Add cache save step (runs even on test/packaging failure)
- Enhance ccache diagnostics with pre/post build stats and cache size
- Release builds fall back to main branch build cache for warm starts

.gitea/workflows/build.yml

@@ -13,11 +13,12 @@ jobs:
     runs-on: app-builder
 
     env:
-      CCACHE_DIR: ${{ github.workspace }}/../.ccache-kindred-create
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
       CCACHE_COMPRESS: "true"
       CCACHE_COMPRESSLEVEL: "6"
       CCACHE_MAXSIZE: "4G"
       CCACHE_SLOPPINESS: "include_file_ctime,include_file_mtime,pch_defines,time_macros"
+      CCACHE_BASEDIR: ${{ github.workspace }}
 
     steps:
       - name: Trust FreeIPA CA certificate
@@ -64,12 +65,26 @@ jobs:
           fi
           pixi --version
 
+      - name: Restore ccache
+        id: ccache-restore
+        uses: https://github.com/actions/cache/restore@v4
+        with:
+          path: ${{ github.workspace }}/.ccache
+          key: ccache-build-${{ github.ref_name }}-${{ github.sha }}
+          restore-keys: |
+            ccache-build-${{ github.ref_name }}-
+            ccache-build-main-
+
       - name: Prepare ccache
         shell: bash
         run: |
           mkdir -p $CCACHE_DIR
           pixi run ccache -z
+          echo "=== ccache configuration ==="
           pixi run ccache -p
+          echo ""
+          echo "=== ccache status before build ==="
+          pixi run ccache -s
 
       - name: Configure (CMake)
         shell: bash
@@ -80,7 +95,20 @@ jobs:
         run: pixi run cmake --build build/release -j$(nproc)
 
       - name: Show ccache statistics
-        run: pixi run ccache -s
+        shell: bash
+        run: |
+          echo "=== ccache statistics after build ==="
+          pixi run ccache -s
+          echo ""
+          echo "=== ccache cache directory size ==="
+          du -sh $CCACHE_DIR
+
+      - name: Save ccache
+        if: always()
+        uses: https://github.com/actions/cache/save@v4
+        with:
+          path: ${{ github.workspace }}/.ccache
+          key: ccache-build-${{ github.ref_name }}-${{ github.sha }}
 
       - name: Run C++ unit tests
         shell: bash

.gitea/workflows/release.yml

@@ -16,11 +16,12 @@ jobs:
     runs-on: app-builder
 
     env:
-      CCACHE_DIR: ${{ github.workspace }}/../.ccache-kindred-create
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
       CCACHE_COMPRESS: "true"
       CCACHE_COMPRESSLEVEL: "6"
       CCACHE_MAXSIZE: "4G"
       CCACHE_SLOPPINESS: "include_file_ctime,include_file_mtime,pch_defines,time_macros"
+      CCACHE_BASEDIR: ${{ github.workspace }}
       BUILD_TAG: ${{ github.ref_name || inputs.tag }}
       MAKE_INSTALLER: "true"
       CFLAGS: "-O3"
@@ -72,11 +73,26 @@ jobs:
           fi
           pixi --version
 
+      - name: Restore ccache
+        id: ccache-restore
+        uses: https://github.com/actions/cache/restore@v4
+        with:
+          path: ${{ github.workspace }}/.ccache
+          key: ccache-release-${{ github.ref_name }}-${{ github.sha }}
+          restore-keys: |
+            ccache-release-
+            ccache-build-main-
+
       - name: Prepare ccache
         shell: bash
         run: |
           mkdir -p $CCACHE_DIR
           pixi run ccache -z
+          echo "=== ccache configuration ==="
+          pixi run ccache -p
+          echo ""
+          echo "=== ccache status before build ==="
+          pixi run ccache -s
 
       - name: Write version info
         run: python3 package/scripts/write_version_info.py ../freecad_version.txt
@@ -88,7 +104,20 @@ jobs:
           pixi run -e package create_bundle
 
       - name: Show ccache statistics
-        run: pixi run ccache -s
+        shell: bash
+        run: |
+          echo "=== ccache statistics after build ==="
+          pixi run ccache -s
+          echo ""
+          echo "=== ccache cache directory size ==="
+          du -sh $CCACHE_DIR
+
+      - name: Save ccache
+        if: always()
+        uses: https://github.com/actions/cache/save@v4
+        with:
+          path: ${{ github.workspace }}/.ccache
+          key: ccache-release-${{ github.ref_name }}-${{ github.sha }}
 
       - name: Build .deb package
         shell: bash