diff --git a/scripts/common/lib.sh b/scripts/common/lib.sh
index c77b775..bc812ad 100755
--- a/scripts/common/lib.sh
+++ b/scripts/common/lib.sh
@@ -63,17 +63,18 @@ health_check() {
 # -----------------------------------------------------------------------------
 
 git_commit() {
-  cd "$ROOT_DIR" || return 1
-  git rev-parse --short HEAD 2>/dev/null || echo "unknown"
+  ( cd "$ROOT_DIR" && git rev-parse --short HEAD 2>/dev/null || echo "unknown" )
 }
 
 git_dirty() {
-  cd "$ROOT_DIR" || return 1
-  if [[ -n "$(git status --porcelain 2>/dev/null)" ]]; then
-    echo "dirty"
-  else
-    echo "clean"
-  fi
+  (
+    cd "$ROOT_DIR" || exit 1
+    if [[ -n "$(git status --porcelain 2>/dev/null)" ]]; then
+      echo "dirty"
+    else
+      echo "clean"
+    fi
+  )
 }
 
 # -----------------------------------------------------------------------------
@@ -96,28 +97,34 @@ write_metadata_json() {
 
   mkdir -p "$(dirname "$output_path")"
 
-  cat > "$output_path" <<EOF
-{
-  "metadata": {
-    "experiment": "${experiment}",
-    "run_id": "${run_id}",
-    "timestamp": "$(date --iso-8601=seconds)",
-    "model": "${model}",
-    "backend": "${backend}",
-    "engine": "${engine}",
-    "hardware": "${hardware}",
-    "accelerator": "${accelerator}",
-    "chip": "${chip}",
-    "script": "${script}",
-    "env": "${env_path}",
-    "git_commit": "$(git_commit)",
-    "git_dirty": "$(git_dirty)",
-    "description": "${description}"
-  },
-  "config": {},
-  "scenarios": []
+  "${PYTHON:-python3}" - "$output_path" "$experiment" "$run_id" "$model" "$backend" "$engine" "$hardware" "$accelerator" "$chip" "$script" "$env_path" "$description" "$(date --iso-8601=seconds)" "$(git_commit)" "$(git_dirty)" <<'PY'
+import json, sys
+(out, experiment, run_id, model, backend, engine, hardware, accelerator,
+ chip, script, env_path, description, timestamp, git_commit,
+ git_dirty) = sys.argv[1:16]
+data = {
+    "metadata": {
+        "experiment": experiment,
+        "run_id": run_id,
+        "timestamp": timestamp,
+        "model": model,
+        "backend": backend,
+        "engine": engine,
+        "hardware": hardware,
+        "accelerator": accelerator,
+        "chip": chip,
+        "script": script,
+        "env": env_path,
+        "git_commit": git_commit,
+        "git_dirty": git_dirty,
+        "description": description,
+    },
+    "config": {},
+    "scenarios": [],
 }
-EOF
+with open(out, "w", encoding="utf-8") as f:
+    json.dump(data, f, indent=2, ensure_ascii=False)
+PY
 }
 
 # -----------------------------------------------------------------------------