refactor(application): fix 4 code smells — validate username input, extract ownership guard and dedup helpers

crates/application/src/services/notification_event.rs

@@ -5,7 +5,7 @@ use domain::{
     events::DomainEvent,
     models::notification::{Notification, NotificationType},
     ports::{NotificationRepository, ThoughtRepository},
-    value_objects::NotificationId,
+    value_objects::{NotificationId, UserId},
 };
 
 pub struct NotificationEventService {
@@ -13,6 +13,10 @@ pub struct NotificationEventService {
     pub notifications: Arc<dyn NotificationRepository>,
 }
 
+fn is_self_action(thought_author: &UserId, actor: &UserId) -> bool {
+    thought_author == actor
+}
+
 impl NotificationEventService {
     pub async fn process(&self, event: &DomainEvent) -> Result<(), DomainError> {
         match event {
@@ -21,7 +25,7 @@ impl NotificationEventService {
                     Some(t) => t,
                     None => return Ok(()),
                 };
-                if thought.user_id == *user_id { return Ok(()); }
+                if is_self_action(&thought.user_id, user_id) { return Ok(()); }
                 self.notifications.save(&Notification {
                     id: NotificationId::new(),
                     user_id: thought.user_id,
@@ -37,7 +41,7 @@ impl NotificationEventService {
                     Some(t) => t,
                     None => return Ok(()),
                 };
-                if thought.user_id == *user_id { return Ok(()); }
+                if is_self_action(&thought.user_id, user_id) { return Ok(()); }
                 self.notifications.save(&Notification {
                     id: NotificationId::new(),
                     user_id: thought.user_id,
@@ -68,7 +72,7 @@ impl NotificationEventService {
                     Some(t) => t,
                     None => return Ok(()),
                 };
-                if original.user_id == *user_id { return Ok(()); }
+                if is_self_action(&original.user_id, user_id) { return Ok(()); }
                 self.notifications.save(&Notification {
                     id: NotificationId::new(),
                     user_id: original.user_id,