fix(activitypub-base): deterministic announce IDs so Undo(Announce) can reference original activity

crates/adapters/activitypub-base/src/service.rs

@@ -175,8 +175,19 @@ impl ActivityPubService {
             return Ok(());
         }
 
+        // Deterministic ID so Undo(Announce) can reference this same activity.
+        let announce_id = url::Url::parse(&format!(
+            "{}/activities/announce/{}",
+            self.base_url,
+            uuid::Uuid::new_v5(
+                &uuid::Uuid::NAMESPACE_URL,
+                format!("{}/{}", local_user_id, object_ap_id).as_bytes(),
+            )
+        ))
+        .map_err(|e| anyhow::anyhow!("{e}"))?;
+
         let announce = crate::activities::AnnounceActivity {
-            id: crate::urls::activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?,
+            id: announce_id,
             kind: Default::default(),
             actor: activitypub_federation::fetch::object_id::ObjectId::from(local_actor.ap_id.clone()),
             object: object_ap_id,
@@ -235,6 +246,17 @@ impl ActivityPubService {
             return Ok(());
         }
 
+        // Reconstruct the same deterministic announce ID used when the boost was sent.
+        let announce_id = url::Url::parse(&format!(
+            "{}/activities/announce/{}",
+            self.base_url,
+            uuid::Uuid::new_v5(
+                &uuid::Uuid::NAMESPACE_URL,
+                format!("{}/{}", local_user_id, object_ap_id).as_bytes(),
+            )
+        ))
+        .map_err(|e| anyhow::anyhow!("{e}"))?;
+
         let undo_id = crate::urls::activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?;
         let undo = crate::activities::UndoActivity {
             id: undo_id,
@@ -242,6 +264,7 @@ impl ActivityPubService {
             actor: activitypub_federation::fetch::object_id::ObjectId::from(local_actor.ap_id.clone()),
             object: serde_json::json!({
                 "type": "Announce",
+                "id": announce_id.to_string(),
                 "actor": local_actor.ap_id.to_string(),
                 "object": object_ap_id.to_string(),
             }),

crates/application/src/services/federation_event.rs

@@ -414,6 +414,21 @@ mod tests {
         assert_eq!(undo_announced[0], "https://mastodon.social/users/bob/statuses/456");
     }
 
+    #[tokio::test]
+    async fn boost_removed_does_not_broadcast_if_thought_missing() {
+        let store = TestStore::default();
+        let alice = alice();
+        let spy = Arc::new(SpyPort::default());
+        svc(&store, spy.clone())
+            .process(&DomainEvent::BoostRemoved {
+                user_id: alice.id.clone(),
+                thought_id: ThoughtId::new(), // doesn't exist in store
+            })
+            .await
+            .unwrap();
+        assert!(spy.undo_announced.lock().unwrap().is_empty());
+    }
+
     #[tokio::test]
     async fn thought_updated_does_not_broadcast_if_user_missing() {
         let store = TestStore::default();