fix(dwh): align adapter sampling contract

harness/tht/rest/execute.py

@@ -17,6 +17,8 @@ from tht.rest.explain import parse_text_plan
 def run_controlled_rest(client, sql: str, *, limit: int) -> ExecResult:
     # Guard read-only client-side anche sul path REST (D7): non delegare l'unica verifica
     # al server. Stesso check strutturale del path diretto.
+    if limit <= 0:
+        raise ValueError("limit must be a positive integer")
     assert_read_only(sql)
     final_sql, injected = _inject_limit(sql, limit)
     start = time.monotonic()
@@ -46,14 +48,3 @@ def explain_rest(client, sql: str) -> PlanSummary:
     except RestError as e:
         raise ExecutionError(str(e)) from e
     return parse_text_plan(lines)
-
-
-def sample_column_rest(
-    client, schema: str, table: str, column: str, *, limit: int
-) -> list[object]:
-    rows = client.top_values(schema, table, column, limit)
-    return [row["value"] for row in rows if row.get("value") is not None]
-
-
-def distinct_values_rest(client, schema: str, table: str, column: str) -> list[object]:
-    return sample_column_rest(client, schema, table, column, limit=1000)