test persistent cache across runs

.github/workflows/build.yaml

@@ -27,30 +27,41 @@ jobs:
   submodule_cache:
     name: Initialize submodule cache
     runs-on: ubuntu-latest
+    outputs:
+      key: ${{ steps.keygen.outputs.smcache_key }}
     steps:
       - uses: actions/checkout@v4
 
       - name: Remove unneeded frameworks to recover disk space
         run: sudo ./.github/cleanup-rootfs.sh
 
+      - name: Generate submodule cache key
+        id: keygen
+        run: echo "smcache_key=smcache-$(printf $(git submodule | sha1sum))" >> $GITHUB_OUTPUT
+
+      - name: Setup submodule cache
+        id: smcache
+        uses: actions/cache@v4
+        with:
+          enableCrossOsArchive: true
+          path: ${{ env.submodule_paths }}
+          key: ${{ steps.keygen.outputs.smcache_key }}
+
       - name: Checkout required submodules
+        if: steps.smcache.outputs.cache-hit != 'true'
         run: git submodule update --init -j $(nproc) --depth 1 $(echo ${submodule_paths} | sed '$d' | tr '\n' ' ')
 
       - name: Storage size optimization
+        if: steps.smcache.outputs.cache-hit != 'true'
         run: |
           echo "Submodules env var: ${submodule_paths}"
           git submodule foreach 'git maintenance run'
 
-      - name: Setup submodule cache
-        uses: actions/cache@v4
-        with:
-          enableCrossOsArchive: true
-          path: ${{ env.submodule_paths }}
-          key: submodule-cache-${{ github.run_id }}-${{ github.run_attempt }}
-
   build:
     runs-on: ${{ matrix.os }}
     needs: [submodule_cache]
+    env:
+      smcache_key: ${{ needs.submodule_cache.outputs.key }}
     strategy:
       matrix:
         os:     [ubuntu-22.04, ubuntu-24.04]
@@ -76,7 +87,7 @@ jobs:
         with:
           enableCrossOsArchive: true
           path: ${{ env.submodule_paths }}
-          key: submodule-cache-${{ github.run_id }}-${{ github.run_attempt }}
+          key: ${{ env.smcache_key }}
 
       - name: build toolchain
         run: |
@@ -129,6 +140,8 @@ jobs:
   test-sim:
     runs-on: ${{ matrix.os }}
     needs: [submodule_cache]
+    env:
+      smcache_key: ${{ needs.submodule_cache.outputs.key }}
     strategy:
       matrix:
         os:     [ubuntu-24.04]
@@ -149,7 +162,7 @@ jobs:
         with:
           enableCrossOsArchive: true
           path: ${{ env.submodule_paths }}
-          key: submodule-cache-${{ github.run_id }}-${{ github.run_attempt }}
+          key: ${{ env.smcache_key }}
 
       - name: build toolchain
         run: |