feat: emit OutboundFollowAccepted when remote accepts our follow

v0.4.2 — consumers can now react to outbound follow acceptance
(e.g. import_remote_outbox to backfill). Previously the accept
handler silently updated the DB with no event for consumers.

src/activities/accept.rs

@@ -49,14 +49,32 @@ impl Activity for AcceptActivity {
         }
         let local_user_id = crate::urls::extract_user_id_from_url(self.object.actor.inner())
             .ok_or_else(|| Error::bad_request(anyhow::anyhow!("invalid actor URL in Follow")))?;
+        let remote_actor_url = self.actor.inner().as_str().to_string();
         data.follow_repo
             .update_following_status(
                 local_user_id,
-                self.actor.inner().as_str(),
+                &remote_actor_url,
                 FollowingStatus::Accepted,
             )
             .await?;
-        tracing::info!(remote_actor = %self.actor.inner(), "follow accepted by remote");
+        tracing::info!(remote_actor = %remote_actor_url, "follow accepted by remote");
+
+        if let Some(publisher) = &data.event_publisher {
+            let outbox_url = data
+                .actor_repo
+                .get_remote_actor(&remote_actor_url)
+                .await
+                .ok()
+                .flatten()
+                .and_then(|a| a.outbox_url);
+            let _ = publisher
+                .publish(crate::data::FederationEvent::OutboundFollowAccepted {
+                    local_user_id,
+                    remote_actor_url,
+                    outbox_url,
+                })
+                .await;
+        }
         Ok(())
     }
 }

src/data.rs

@@ -41,6 +41,13 @@ pub enum FederationEvent {
         owner_user_id: uuid::Uuid,
         follower_inbox_url: String,
     },
+    /// A remote actor accepted our outbound follow request.
+    /// Call `ActivityPubService::import_remote_outbox(outbox_url, actor_url)` to backfill.
+    OutboundFollowAccepted {
+        local_user_id: uuid::Uuid,
+        remote_actor_url: String,
+        outbox_url: Option<String>,
+    },
 }
 
 /// Receives typed federation events.