Handle null prefer in inline routing policy

crates/brightstaff/src/handlers/routing_service.rs

@@ -27,8 +27,9 @@ pub fn extract_routing_policy(
     let routing_preferences = json_body
         .as_object_mut()
         .and_then(|o| o.remove("routing_preferences"))
-        .and_then(
-            |value| match serde_json::from_value::<Vec<TopLevelRoutingPreference>>(value) {
+        .and_then(|mut value| {
+            normalize_null_prefer_to_none(&mut value);
+            match serde_json::from_value::<Vec<TopLevelRoutingPreference>>(value) {
                 Ok(prefs) => {
                     info!(
                         num_routes = prefs.len(),
@@ -40,13 +41,43 @@ pub fn extract_routing_policy(
                     warn!(error = %err, "failed to parse routing_preferences");
                     None
                 }
-            },
-        );
+            }
+        });
 
     let bytes = Bytes::from(serde_json::to_vec(&json_body).unwrap());
     Ok((bytes, routing_preferences))
 }
 
+fn normalize_null_prefer_to_none(routing_preferences: &mut serde_json::Value) {
+    let Some(preferences) = routing_preferences.as_array_mut() else {
+        return;
+    };
+
+    for preference in preferences {
+        let Some(preference_obj) = preference.as_object_mut() else {
+            continue;
+        };
+
+        let Some(selection_policy) = preference_obj.get_mut("selection_policy") else {
+            continue;
+        };
+
+        let Some(policy_obj) = selection_policy.as_object_mut() else {
+            continue;
+        };
+
+        if policy_obj
+            .get("prefer")
+            .is_some_and(serde_json::Value::is_null)
+        {
+            policy_obj.insert(
+                "prefer".to_string(),
+                serde_json::Value::String("none".to_string()),
+            );
+        }
+    }
+}
+
 #[derive(serde::Serialize)]
 struct RoutingDecisionResponse {
     /// Ranked model list — use first, fall back to next on 429/5xx.
@@ -197,6 +228,7 @@ async fn routing_decision_inner(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use common::configuration::SelectionPreference;
 
     fn make_chat_body(extra_fields: &str) -> Vec<u8> {
         let extra = if extra_fields.is_empty() {
@@ -264,6 +296,24 @@ mod tests {
         assert!(cleaned_json.get("routing_preferences").is_none());
     }
 
+    #[test]
+    fn extract_routing_policy_prefer_null_defaults_to_none() {
+        let policy = r#""routing_preferences": [
+            {
+                "name": "coding",
+                "description": "code generation, writing functions, debugging",
+                "models": ["openai/gpt-4o", "openai/gpt-4o-mini"],
+                "selection_policy": {"prefer": null}
+            }
+        ]"#;
+        let body = make_chat_body(policy);
+        let (_cleaned, prefs) = extract_routing_policy(&body).unwrap();
+
+        let prefs = prefs.expect("should parse routing_preferences when prefer is null");
+        assert_eq!(prefs.len(), 1);
+        assert_eq!(prefs[0].selection_policy.prefer, SelectionPreference::None);
+    }
+
     #[test]
     fn routing_decision_response_serialization() {
         let response = RoutingDecisionResponse {