refactor(application): move local/remote follow routing out of presentation handler

crates/application/src/use_cases/social.rs

@@ -3,8 +3,11 @@ use domain::{
     errors::DomainError,
     events::DomainEvent,
     models::social::{Block, Boost, Follow, FollowState, Like},
-    ports::{BlockRepository, BoostRepository, EventPublisher, FollowRepository, LikeRepository},
-    value_objects::{BoostId, LikeId, ThoughtId, UserId},
+    ports::{
+        BlockRepository, BoostRepository, EventPublisher, FederationActionPort, FollowRepository,
+        LikeRepository, UserRepository,
+    },
+    value_objects::{BoostId, LikeId, ThoughtId, UserId, Username},
 };
 
 pub async fn like_thought(
@@ -87,6 +90,27 @@ pub async fn unboost_thought(
     Ok(())
 }
 
+pub async fn follow_actor(
+    follows: &dyn FollowRepository,
+    users: &dyn UserRepository,
+    federation: &dyn FederationActionPort,
+    events: &dyn EventPublisher,
+    follower_id: &UserId,
+    username: &str,
+) -> Result<(), DomainError> {
+    if username.contains('@') {
+        federation.follow_remote(follower_id, username).await
+    } else {
+        let uname = Username::new(username)
+            .map_err(|_| DomainError::InvalidInput("invalid username".into()))?;
+        let target = users
+            .find_by_username(&uname)
+            .await?
+            .ok_or(DomainError::NotFound)?;
+        follow_user(follows, events, follower_id, &target.id).await
+    }
+}
+
 pub async fn follow_user(
     follows: &dyn FollowRepository,
     events: &dyn EventPublisher,
@@ -315,6 +339,37 @@ mod tests {
         assert!(matches!(err, DomainError::InvalidInput(_)));
     }
 
+    #[tokio::test]
+    async fn follow_actor_local_routes_to_follow_user() {
+        let store = TestStore::default();
+        let alice = user("alice");
+        let bob = user("bob");
+        store.users.lock().unwrap().push(bob.clone());
+        follow_actor(&store, &store, &store, &store, &alice.id, "bob")
+            .await
+            .unwrap();
+        assert_eq!(store.follows.lock().unwrap().len(), 1);
+    }
+
+    #[tokio::test]
+    async fn follow_actor_remote_routes_to_federation() {
+        let store = TestStore::default();
+        let alice = user("alice");
+        follow_actor(
+            &store,
+            &store,
+            &store,
+            &store,
+            &alice.id,
+            "@bob@example.com",
+        )
+        .await
+        .unwrap();
+        // TestStore.follow_remote is a no-op that returns Ok(())
+        // no local follow should be recorded
+        assert!(store.follows.lock().unwrap().is_empty());
+    }
+
     #[tokio::test]
     async fn boost_and_unboost() {
         let store = TestStore::default();

crates/presentation/src/handlers/social.rs

@@ -57,12 +57,15 @@ pub async fn post_follow(
     AuthUser(uid): AuthUser,
     Path(username): Path<String>,
 ) -> Result<StatusCode, ApiError> {
-    if username.contains('@') {
-        s.federation.follow_remote(&uid, &username).await?;
-    } else {
-        let target = get_user_by_username(&*s.users, &username).await?;
-        follow_user(&*s.follows, &*s.events, &uid, &target.id).await?;
-    }
+    follow_actor(
+        &*s.follows,
+        &*s.users,
+        &*s.federation,
+        &*s.events,
+        &uid,
+        &username,
+    )
+    .await?;
     Ok(StatusCode::NO_CONTENT)
 }
 #[utoipa::path(