fix: deduplicate null_as_empty_vec and normalize user_order channel name

src/models/common.rs

@@ -110,6 +110,22 @@ pub fn cents_to_dollars(cents: i64) -> f64 {
     cents as f64 / 100.0
 }
 
+/// Custom deserializer that treats `null` as an empty `Vec`.
+///
+/// The Kalshi API sometimes returns `null` instead of `[]` for empty arrays.
+/// Use with `#[serde(default, deserialize_with = "null_as_empty_vec::deserialize")]`.
+pub(crate) mod null_as_empty_vec {
+    use serde::{Deserialize, Deserializer};
+
+    pub fn deserialize<'de, D, T>(deserializer: D) -> Result<Vec<T>, D::Error>
+    where
+        D: Deserializer<'de>,
+        T: Deserialize<'de>,
+    {
+        Ok(Option::<Vec<T>>::deserialize(deserializer)?.unwrap_or_default())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/models/market.rs

@@ -542,19 +542,7 @@ mod orderbook_serde {
     }
 }
 
-/// Custom deserializer for Vec that treats null as empty.
-mod null_as_empty_vec {
-    use serde::{Deserialize, Deserializer};
-
-    pub fn deserialize<'de, D, T>(deserializer: D) -> Result<Vec<T>, D::Error>
-    where
-        D: Deserializer<'de>,
-        T: Deserialize<'de>,
-    {
-        let opt: Option<Vec<T>> = Option::deserialize(deserializer)?;
-        Ok(opt.unwrap_or_default())
-    }
-}
+use super::common::null_as_empty_vec;
 
 /// An orderbook for a market.
 #[derive(Debug, Clone, Default, Serialize, Deserialize)]

src/models/order.rs

@@ -975,17 +975,7 @@ impl GetQueuePositionsParams {
     }
 }
 
-mod null_as_empty_vec {
-    use serde::{Deserialize, Deserializer};
-
-    pub fn deserialize<'de, D, T>(deserializer: D) -> Result<Vec<T>, D::Error>
-    where
-        D: Deserializer<'de>,
-        T: Deserialize<'de>,
-    {
-        Ok(Option::<Vec<T>>::deserialize(deserializer)?.unwrap_or_default())
-    }
-}
+use super::common::null_as_empty_vec;
 
 #[cfg(test)]
 mod tests {

src/ws/session.rs

@@ -838,6 +838,13 @@ impl KalshiStreamSession {
             }
 
             Ok(IncomingMessage::Update { msg_type, sid, msg }) => {
+                // Normalize API aliases to canonical channel names.
+                // The Kalshi API sends "user_order" (singular) for order updates,
+                // but the channel is subscribed as "user_orders" (plural).
+                let msg_type = match msg_type.as_str() {
+                    "user_order" => "user_orders".to_string(),
+                    _ => msg_type,
+                };
                 debug!("Update on sid {}: type={}", sid, msg_type);
 
                 // Handle "unsubscribed" updates specially