fix(dwh): validate adapter limits strictly

harness/tht/rest/execute.py

@@ -9,7 +9,14 @@ il client mantiene solo l'iniezione del LIMIT (per il rilevamento del troncament
 
 import time
 
-from tht.execute import ExecResult, ExecutionError, PlanSummary, _inject_limit, assert_read_only
+from tht.execute import (
+    ExecResult,
+    ExecutionError,
+    PlanSummary,
+    _inject_limit,
+    assert_read_only,
+    require_positive_int,
+)
 from tht.rest.client import RestError
 from tht.rest.explain import parse_text_plan
 
@@ -17,8 +24,7 @@ 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")
+    limit = require_positive_int(limit, name="limit")
     assert_read_only(sql)
     final_sql, injected = _inject_limit(sql, limit)
     start = time.monotonic()