better commit hash handling

docker/build.sh

@@ -44,13 +44,33 @@ if [ "$COMMIT" == "$(git rev-parse --short HEAD)" ]; then
     fi
 fi
 
+check_remote_commit_exists() {
+    # Usage: check_remote_commit_exists <repo-url> <commit-sha>
+    local url="$1"
+    local commit="$2"
+
+    # Create a temporary directory for a shallow fetch
+    local tmpdir
+    tmpdir="$(mktemp -d)"
+    trap 'rm -rf "$tmpdir"' RETURN  # auto-cleanup on function exit
+
+    git -C "$tmpdir" init -q
+    git -C "$tmpdir" remote add origin "$url"
+
+    if git -C "$tmpdir" fetch --quiet --depth=1 origin "$commit" 2>/dev/null; then
+        echo "✅ Commit $commit exists on remote."
+        return 0
+    else
+        echo "❌ ERROR: Commit $commit not found on remote."
+        echo "Refs currently visible on remote:"
+        git ls-remote --heads --tags "$url"
+        return 1
+    fi
+}
+
 # check if the commit has been pushed
-REMOTE_COMMIT=$(git ls-remote https://github.com/jkiesele/minicalosim | grep $COMMIT)
-if [ -z "$REMOTE_COMMIT" ]; then
+if ! check_remote_commit_exists https://github.com/jkiesele/minicalosim $COMMIT; then
     echo "ERROR: Commit $COMMIT not found in remote repository."
-       echo only found commits:
-         git ls-remote https://github.com/jkiesele/minicalosim
-       exit 1
 fi
 
 # check if no-cache is given as second argument