Communities follow FEP-1b12, circles federate to their members only

Communities:
- a post addressed to a community (to, cc or audience) is accepted
  according to its posting policy - followers, anyone, or moderators -
  and GroupDistributor announces the whole activity with `audience` to
  the community's followers, plus the object for new posts so Mastodon
  shows them; updates and deletes of community content are announced too;
- top-level posts are Pages with a name (the title, or a headline from
  the text); /flock counts members, /wardens lists moderators;
- a Mastodon client posts into a community by mentioning it, or into a
  remote group, which sets `audience`;
- an Announce of an activity from a remote group a persona follows (Lemmy)
  is followed through: the object is fetched from its own origin, kept with
  its AudienceURI, and fanned out to the group's local followers; updates
  are applied in place and deletes checked against the origin.

Circles stop being local-only: an undiscoverable Group actor whose follows
are all requests the owner approves; posts addressed to the circle and its
/flock and delivered to members' own inboxes, never announced, never
public; a remote member's post into the circle is accepted from members
only. SignedFetchAuthorizer serves circle posts and collections only to a
signed request from a member or a member server's instance actor - 404 for
anyone else. Circles never surface in search, lookups, mentions, account
ids or profile pages.

Federation:SecureMode requires a valid signature on every GET under
/peasants except the instance actor. Group forms take a posting policy.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Federation/Inbox/Handlers/DeleteHandler.cs

@@ -26,9 +26,12 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		readonly ILocalActorService _localActors;
 		readonly IRemoteActorService _remoteActors;
 		readonly IDeliveryService _delivery;
+		readonly IGroupDistributor _groups;
 
-		public DeleteHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IDeliveryService delivery)
+		public DeleteHandler(DbEntities dbEntities, ILocalActorService localActors, IRemoteActorService remoteActors, IDeliveryService delivery,
+			IGroupDistributor groups)
 		{
+			_groups = groups;
 			_dbEntities = dbEntities;
 			_localActors = localActors;
 			_remoteActors = remoteActors;
@@ -67,6 +70,8 @@ namespace PrivaPub.Federation.Inbox.Handlers
 				return;
 			await DB.Default.DeleteAsync<PostEntity>(post.ID);
 			await DB.Default.DeleteAsync<TimelineEntry>(e => e.PostId == post.ID || e.ReblogOfPostId == post.ID);
+			if (!string.IsNullOrEmpty(post.GroupId) && await _localActors.FindById(LocalActorKind.Group, post.GroupId, token) is { IsCircle: false } community)
+				await _groups.Announce(community, activity.AsObject(), post.ObjectURI, isNewPost: false, token);
 			await DB.Default.DeleteAsync<PostEntity>(p => p.ReblogOfPostId == post.ID);
 			if (!string.IsNullOrEmpty(post.AnsweringToPostId))
 				await DB.Default.Update<PostEntity>().MatchID(post.AnsweringToPostId).Modify(b => b.Inc(p => p.RepliesCount, -1)).ExecuteAsync(token);