fix: validate prediction feature dimensions

api/core/model.py

@@ -9,7 +9,11 @@
 
 
 class SentinelModel(nn.Module):
-    """Two-layer MLP that accepts arbitrary-length feature vectors."""
+    """Two-layer MLP with a fixed-width input contract per model instance.
+
+    The default model expects 16 features. Deployments using a different
+    input dimension must update the API contract and model artifact together.
+    """
 
     def __init__(self, input_dim: int = 16, hidden_dim: int = 32, output_dim: int = 1) -> None:
         super().__init__()

api/main.py

@@ -6,7 +6,7 @@
 from slowapi.util import get_remote_address
 from slowapi.errors import RateLimitExceeded
 from api.inference import run_inference
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import List, Optional
 
 limiter = Limiter(key_func=get_remote_address)
@@ -16,8 +16,16 @@
 app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler)
 
 
+FEATURE_DIMENSIONS = 16
+
 class RequestModel(BaseModel):
-    features: List[float]
+    """Fixed-width feature vector required by the shipped SentinelModel."""
+
+    features: List[float] = Field(
+        min_length=FEATURE_DIMENSIONS,
+        max_length=FEATURE_DIMENSIONS,
+        description="Exactly 16 numeric features in the model's expected order.",
+    )
 
 
 class PromptRequest(BaseModel):

tests/test_predict.py

@@ -0,0 +1,17 @@
+from api import main
+
+
+def test_predict_accepts_exact_model_feature_dimension(client, monkeypatch):
+    monkeypatch.setattr(main, "run_inference", lambda features: [0.42])
+
+    response = client.post("/predict", json={"features": [0.0] * 16})
+
+    assert response.status_code == 200
+    assert response.json() == {"prediction": [0.42]}
+
+
+def test_predict_rejects_feature_vectors_with_the_wrong_dimension(client):
+    response = client.post("/predict", json={"features": [0.0] * 15})
+
+    assert response.status_code == 422
+    assert any(error["loc"] == ["body", "features"] for error in response.json()["detail"])