run_eval: construct the judge only when the recipe uses llm_judge

Co-Authored-By: Claude <noreply@anthropic.com>

evalharness/model/runner.py

@@ -821,7 +821,8 @@ async def run_eval(
                 status_callback('Scores cached in checkpoint -- replaying '
                                 '(no scorers run; --rescore re-evaluates)')
 
-    if judge is None and judge_spec and _records is None:
+    if judge is None and judge_spec and _records is None \
+            and _recipe_needs_judge(recipe):
         if status_callback:
             status_callback('loading judge model')
         judge_adapter = _make_adapter(judge_spec, api_key=judge_api_key or api_key)
@@ -893,6 +894,20 @@ async def run_eval(
     return report
 
 
+def _recipe_needs_judge(recipe) -> bool:
+    """Only construct the judge when a scorer actually consumes it --
+    rule-based benches (longbench_v2 etc.) never touch a judge, and
+    building one there crashed on malformed specs for no benefit."""
+    try:
+        for spec in (recipe.scorers or {}).values():
+            p = spec if isinstance(spec, dict) else {}
+            if p.get('name') in ('llm_judge', 'judge'):
+                return True
+    except Exception:
+        pass
+    return False
+
+
 def _env_user_adapter(spec: str):
     """Build (once per spec) the separate USER-simulator adapter for env
     benches (tau2 strong-user parity mode)."""