Merge pull request #956 from newtonick/fix-build-yml-versioning

### .github/workflows/build.yml
@@ -83,15 +83,9 @@ jobs:
             echo "img_version=os${os_version}_sw${source_version}"| tee -a $GITHUB_ENV
           fi
 
-      - name: delete unnecessary files
-        # The seedsigner-os buildroot overlay only needs src/; drop everything
-        # else from the seedsigner checkout (tests, docs, tooling, .git, etc.)
-        # to keep the overlay minimal.
-        run: |
-          cd seedsigner-os/opt/rootfs-overlay/opt
-          find . -mindepth 1 -maxdepth 1 ! -name src -exec rm -rf {} +
-          ls -la .
-          ls -la src
+      # NOTE: trimming the overlay down to src/ is deliberately left to seedsigner-os
+      # build.sh (delete_unnecessary_files). It needs the .git/ and tools/ we would
+      # otherwise delete here in order to write version.json first.
 
       - name: restore build cache
         uses: actions/cache@v4
@@ -125,6 +119,15 @@ jobs:
             --${{ matrix.target }} --skip-repo --no-clean
           sudo chown -R $USER:$USER seedsigner-os/images seedsigner-os/buildroot_dl ~/.buildroot-ccache/
 
+      # version.json is written by seedsigner-os build.sh. If it is missing or has a
+      # null field the app raises at the splash screen, which looks like an
+      # unrecoverable boot hang, so fail the build rather than publish the image.
+      - name: verify version.json
+        working-directory: seedsigner-os/opt/rootfs-overlay/opt
+        run: |
+          cat src/seedsigner/version.json
+          jq -e '.name and .fork and .short_commit_hash and .timestamp' src/seedsigner/version.json
+
       - name: list image (before rename)
         run: |
           ls -la seedsigner-os/images