restore mkosi tree cache

Signed-off-by: Alison Schofield <alison.schofield@intel.com>

Author: AlisonSchofield

.github/workflows/main.yml

@@ -166,11 +166,28 @@ jobs:
             git clone --depth 1 --branch "$KERNEL_BRANCH" "https://github.com/${KERNEL_REPO}.git" kernel
           fi
 
-      - name: Ensure mkosi apt cache dirs exist
+      - name: Ensure mkosi cache dirs exist
         run: |
+          mkdir -p kernel/qbuild/mkosi.cache
           mkdir -p kernel/qbuild/mkosi.cache/{cache/apt,lib/apt}
 
-      # Cache only mkosi's apt caches (safe + small; avoids rootfs/ssh key permission issues)
+      # Cache mkosi's tree caches (big win: avoids re-installing packages into a fresh rootfs tree)
+      - name: Restore mkosi tree cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            kernel/qbuild/mkosi.cache/ubuntu~noble~x86-64.cache
+            kernel/qbuild/mkosi.cache/ubuntu~noble~x86-64.manifest
+            kernel/qbuild/mkosi.cache/ubuntu~noble~x86-64~default-initrd.cache
+            kernel/qbuild/mkosi.cache/ubuntu~noble~x86-64~default-initrd.manifest
+          key: mkositree_${{ env.RUNNER_OS_LABEL }}_${{ env.ARCH_LABEL }}_${{ env.MKOSI_DISTRO }}_${{ env.MKOSI_RELEASE }}_${{ steps.weeks.outputs.now }}
+          restore-keys: |
+            mkositree_${{ env.RUNNER_OS_LABEL }}_${{ env.ARCH_LABEL }}_${{ env.MKOSI_DISTRO }}_${{ env.MKOSI_RELEASE }}_${{ steps.weeks.outputs.previous }}
+            mkositree_${{ env.RUNNER_OS_LABEL }}_${{ env.ARCH_LABEL }}_${{ env.MKOSI_DISTRO }}_${{ env.MKOSI_RELEASE }}
+            mkositree_${{ env.RUNNER_OS_LABEL }}_${{ env.ARCH_LABEL }}
+          fail-on-cache-miss: false
+
+      # Cache only mkosi's apt caches (nice-to-have)
       - name: Restore mkosi apt cache
         uses: actions/cache@v4
         with:
@@ -184,6 +201,10 @@ jobs:
             mkosiapt_${{ env.RUNNER_OS_LABEL }}_${{ env.ARCH_LABEL }}
           fail-on-cache-miss: false
 
+      - name: Normalize mkosi cache permissions
+        run: |
+          sudo chmod -R a+rX kernel/qbuild/mkosi.cache || true
+
       - name: show revisions under test
         run: |
           echo "Kernel repo:   $KERNEL_REPO"