diff --git a/engine/decision_engine.py b/engine/decision_engine.py
index c396ea0..791ed4e 100644
--- a/engine/decision_engine.py
+++ b/engine/decision_engine.py
@@ -14,7 +14,7 @@ def _constraint_failed(candidate: ScoreResult, constraint: ConstraintSpec) -> bo
         return value < constraint.value
     if constraint.op == "==":
         return value != constraint.value
-    return True
+    raise ValueError(f"unsupported constraint operator: {constraint.op}")
 
 
 def decide_candidate(
@@ -30,7 +30,7 @@ def decide_candidate(
             status="crash",
             reason=f"command failed with exit code {run_result.exit_code}",
             baseline_score=baseline,
-            candidate_score=candidate.primary_score,
+            candidate_score=None,
         )
 
     failed_constraints = [
diff --git a/engine/scorer.py b/engine/scorer.py
index c3a1bf4..a6d7b00 100644
--- a/engine/scorer.py
+++ b/engine/scorer.py
@@ -10,12 +10,12 @@ def parse_score_output(output: str, score_field: str, metrics_field: str) -> Sco
     if not isinstance(parsed, dict):
         raise ValueError("score output must be a JSON object")
 
-    metrics = parsed.get(metrics_field, {})
+    metrics = parsed[metrics_field]
     if not isinstance(metrics, dict):
         raise ValueError(f"{metrics_field} must be a JSON object")
 
     return ScoreResult(
         primary_score=float(parsed[score_field]),
-        metrics=metrics,
+        metrics=dict(metrics),
         raw_output=parsed,
     )