diff --git a/crates/worker/Cargo.toml b/crates/worker/Cargo.toml
index 4901ae8..bb5c47c 100644
--- a/crates/worker/Cargo.toml
+++ b/crates/worker/Cargo.toml
@@ -2,3 +2,26 @@
 name = "worker"
 version = "0.1.0"
 edition = "2021"
+
+[[bin]]
+name = "thoughts-worker"
+path = "src/main.rs"
+
+[dependencies]
+domain        = { workspace = true }
+nats          = { workspace = true }
+event-payload = { workspace = true }
+postgres      = { workspace = true }
+async-nats    = { workspace = true }
+tokio         = { workspace = true, features = ["full"] }
+futures       = { workspace = true }
+async-trait   = { workspace = true }
+tracing       = { workspace = true }
+tracing-subscriber = { workspace = true }
+dotenvy       = { workspace = true }
+serde_json    = { workspace = true }
+chrono        = { workspace = true }
+sqlx          = { workspace = true }
+
+[dev-dependencies]
+domain = { workspace = true, features = ["test-helpers"] }
diff --git a/crates/worker/src/handlers.rs b/crates/worker/src/handlers.rs
new file mode 100644
index 0000000..af61628
--- /dev/null
+++ b/crates/worker/src/handlers.rs
@@ -0,0 +1,178 @@
+use std::sync::Arc;
+use chrono::Utc;
+use domain::{
+    errors::DomainError,
+    events::DomainEvent,
+    models::notification::{Notification, NotificationType},
+    ports::{NotificationRepository, ThoughtRepository},
+    value_objects::NotificationId,
+};
+
+/// Handles domain events that should create notifications for users.
+pub struct NotificationHandler {
+    pub thoughts:      Arc<dyn ThoughtRepository>,
+    pub notifications: Arc<dyn NotificationRepository>,
+}
+
+impl NotificationHandler {
+    pub async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
+        match event {
+            DomainEvent::LikeAdded { like_id: _, user_id, thought_id } => {
+                let thought = match self.thoughts.find_by_id(thought_id).await? {
+                    Some(t) => t,
+                    None => return Ok(()), // thought deleted — skip
+                };
+                if thought.user_id == *user_id { return Ok(()); } // no self-notifications
+                self.notifications.save(&Notification {
+                    id: NotificationId::new(),
+                    user_id: thought.user_id,
+                    notification_type: NotificationType::Like,
+                    from_user_id: Some(user_id.clone()),
+                    thought_id: Some(thought_id.clone()),
+                    read: false,
+                    created_at: Utc::now(),
+                }).await
+            }
+            DomainEvent::BoostAdded { boost_id: _, user_id, thought_id } => {
+                let thought = match self.thoughts.find_by_id(thought_id).await? {
+                    Some(t) => t,
+                    None => return Ok(()),
+                };
+                if thought.user_id == *user_id { return Ok(()); }
+                self.notifications.save(&Notification {
+                    id: NotificationId::new(),
+                    user_id: thought.user_id,
+                    notification_type: NotificationType::Boost,
+                    from_user_id: Some(user_id.clone()),
+                    thought_id: Some(thought_id.clone()),
+                    read: false,
+                    created_at: Utc::now(),
+                }).await
+            }
+            DomainEvent::FollowAccepted { follower_id, following_id } => {
+                // The person being followed (following_id) gets notified
+                self.notifications.save(&Notification {
+                    id: NotificationId::new(),
+                    user_id: following_id.clone(),
+                    notification_type: NotificationType::Follow,
+                    from_user_id: Some(follower_id.clone()),
+                    thought_id: None,
+                    read: false,
+                    created_at: Utc::now(),
+                }).await
+            }
+            // All other events: no notification needed in Plan 3
+            _ => Ok(()),
+        }
+    }
+}
+
+/// Stub handler for ActivityPub federation — implemented in Plan 4.
+pub struct FederationHandler;
+
+impl FederationHandler {
+    pub async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
+        tracing::debug!(?event, "federation handler (stub — Plan 4)");
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use domain::{
+        models::{thought::{Thought, Visibility}, user::User},
+        testing::TestStore,
+        value_objects::*,
+    };
+    use std::sync::Arc;
+
+    fn alice() -> User {
+        User::new_local(
+            UserId::new(),
+            Username::new("alice").unwrap(),
+            Email::new("alice@ex.com").unwrap(),
+            PasswordHash("h".into()),
+        )
+    }
+
+    #[tokio::test]
+    async fn like_added_creates_notification_for_thought_author() {
+        let store = TestStore::default();
+        let alice = alice();
+        let bob_id = UserId::new();
+
+        let thought = Thought::new_local(
+            ThoughtId::new(), alice.id.clone(),
+            Content::new_local("hello").unwrap(),
+            None, Visibility::Public, None, false,
+        );
+        store.users.lock().unwrap().push(alice.clone());
+        store.thoughts.lock().unwrap().push(thought.clone());
+
+        let handler = NotificationHandler {
+            thoughts:      Arc::new(store.clone()),
+            notifications: Arc::new(store.clone()),
+        };
+
+        handler.handle(&DomainEvent::LikeAdded {
+            like_id: LikeId::new(),
+            user_id: bob_id.clone(),
+            thought_id: thought.id.clone(),
+        }).await.unwrap();
+
+        let notifs = store.notifications.lock().unwrap();
+        assert_eq!(notifs.len(), 1);
+        assert_eq!(notifs[0].user_id, alice.id);
+        assert!(matches!(notifs[0].notification_type, NotificationType::Like));
+    }
+
+    #[tokio::test]
+    async fn self_like_does_not_create_notification() {
+        let store = TestStore::default();
+        let alice = alice();
+        let thought = Thought::new_local(
+            ThoughtId::new(), alice.id.clone(),
+            Content::new_local("hello").unwrap(),
+            None, Visibility::Public, None, false,
+        );
+        store.users.lock().unwrap().push(alice.clone());
+        store.thoughts.lock().unwrap().push(thought.clone());
+
+        let handler = NotificationHandler {
+            thoughts:      Arc::new(store.clone()),
+            notifications: Arc::new(store.clone()),
+        };
+
+        handler.handle(&DomainEvent::LikeAdded {
+            like_id: LikeId::new(),
+            user_id: alice.id.clone(),
+            thought_id: thought.id.clone(),
+        }).await.unwrap();
+
+        assert!(store.notifications.lock().unwrap().is_empty());
+    }
+
+    #[tokio::test]
+    async fn follow_accepted_creates_notification() {
+        let store = TestStore::default();
+        let alice = alice();
+        let bob_id = UserId::new();
+        store.users.lock().unwrap().push(alice.clone());
+
+        let handler = NotificationHandler {
+            thoughts:      Arc::new(store.clone()),
+            notifications: Arc::new(store.clone()),
+        };
+
+        handler.handle(&DomainEvent::FollowAccepted {
+            follower_id: bob_id.clone(),
+            following_id: alice.id.clone(),
+        }).await.unwrap();
+
+        let notifs = store.notifications.lock().unwrap();
+        assert_eq!(notifs.len(), 1);
+        assert_eq!(notifs[0].user_id, alice.id);
+        assert!(matches!(notifs[0].notification_type, NotificationType::Follow));
+    }
+}