diff --git a/4-Infrastructure/lib/jsonl.py b/4-Infrastructure/lib/jsonl.py
index 614e2b2e..f1f227a1 100644
--- a/4-Infrastructure/lib/jsonl.py
+++ b/4-Infrastructure/lib/jsonl.py
@@ -23,11 +23,12 @@ def load_jsonl(path: Path) -> list[dict[str, Any]]:
 
 
 def write_jsonl(path: Path, rows: list[dict[str, Any]], *, append: bool = False) -> None:
-    """Write a list of dicts as JSONL."""
+    """Write a list of dicts as JSONL (sorted keys for deterministic output)."""
+    path.parent.mkdir(parents=True, exist_ok=True)
     mode = "a" if append else "w"
     with path.open(mode, encoding="utf-8") as fh:
         for row in rows:
-            fh.write(json.dumps(row, ensure_ascii=False) + "\n")
+            fh.write(json.dumps(row, sort_keys=True, ensure_ascii=False) + "\n")
 
 
 def stable_json(obj: Any) -> str:
diff --git a/4-Infrastructure/lib/q16.py b/4-Infrastructure/lib/q16.py
index e38ad388..62c5b64c 100644
--- a/4-Infrastructure/lib/q16.py
+++ b/4-Infrastructure/lib/q16.py
@@ -38,7 +38,7 @@ def q16_mul(a: int, b: int) -> int:
 def q16_div(a: int, b: int) -> int:
     """Divide two Q16_16 values with normalization."""
     if b == 0:
-        return 0
+        raise ZeroDivisionError("Q16 division by zero")
     return (a * Q16_ONE) // b