Clamp grader scores strictly between 0.001 and 0.999 in endpoint and model

api/server.py

@@ -191,17 +191,19 @@ async def tasks():
 async def grader(request: GraderRequest):
     """
     Grades a completed episode action.
-    Returns float score 0.0-1.0. Never crashes.
-    Edge cases: null action → 0.0, unknown task → 0.0.
+    Returns float score strictly between 0.0 and 1.0 exclusive.
+    Never crashes.
     """
     try:
         if request.action is None:
             return GraderResponse(
-                score     = 0.0,
+                score     = 0.001,
                 feedback  = "No action provided for grading.",
                 breakdown = {"error": "null_action"}
             )
         score, breakdown, feedback = grade(request.action, request.task_id)
+        # Clamp strictly between 0 and 1 exclusive
+        score = max(0.001, min(0.999, score))
         return GraderResponse(
             score     = score,
             feedback  = feedback,
@@ -209,12 +211,11 @@ async def grader(request: GraderRequest):
         )
     except Exception as e:
         return GraderResponse(
-            score     = 0.0,
+            score     = 0.001,
             feedback  = f"Grader error: {str(e)}",
             breakdown = {"error": str(e)}
         )
 
-
 # ─────────────────────────────────────────────
 #  7. /baseline — POST
 # ─────────────────────────────────────────────

env/models.py

@@ -185,10 +185,15 @@ class GraderRequest(BaseModel):
     episode:  Optional[dict]   = None
 
 class GraderResponse(BaseModel):
-    score:    float
+    score:    float = Field(..., gt=0.0, lt=1.0)
     feedback: str
     breakdown: dict
 
+    @field_validator("score")
+    @classmethod
+    def clamp_score(cls, v):
+        return max(0.001, min(0.999, round(v, 4)))
+
 class HealthResponse(BaseModel):
     status:  str = "ok"
     version: str = "1.0.0"