fix(dwh): validate adapter limits strictly

harness/tht/execute/__init__.py

@@ -26,6 +26,13 @@ class PlanSummary:
     node_types: list[str]
 
 
+def require_positive_int(value: object, *, name: str) -> int:
+    """Return a validated positive integer, excluding booleans and numeric lookalikes."""
+    if type(value) is not int or value <= 0:
+        raise ValueError(f"{name} must be a positive integer")
+    return value
+
+
 def _inject_limit(sql: str, limit: int) -> tuple[str, bool]:
     """Aggiunge LIMIT limit+1 se assente (il +1 serve a rilevare il troncamento).
     Se la query ha gia' un suo LIMIT, lo si rispetta."""