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/Api/Mastodon/Controllers/AccountsController.cs

@@ -114,7 +114,7 @@ namespace PrivaPub.Api.Mastodon.Controllers
 			if (parts.Length == 1 || parts[1].Equals(localDomain, StringComparison.OrdinalIgnoreCase))
 			{
 				var local = await _localActors.FindByUserName(parts[0], token);
-				return local is { IsFederated: true, Kind: not LocalActorKind.Application } ? Json(await _mapper.Local(local, false, token)) : NotFoundError();
+				return local is { IsFederated: true, IsCircle: false, Kind: not LocalActorKind.Application } ? Json(await _mapper.Local(local, false, token)) : NotFoundError();
 			}
 			var userName = parts[0];
 			var domain = parts[1].ToLowerInvariant();
@@ -365,7 +365,7 @@ namespace PrivaPub.Api.Mastodon.Controllers
 			if (avatar is { DeletionAt: null })
 				return (_localActors.FromAvatar(avatar), default);
 			var group = await _dbEntities.Groups.MatchID(id).ExecuteFirstAsync(token);
-			if (group is { DeletionAt: null } && _localActors.FromGroup(group) is { IsFederated: true } community)
+			if (group is { DeletionAt: null } && _localActors.FromGroup(group) is { IsFederated: true, IsCircle: false } community)
 				return (community, default);
 			return (default, await _dbEntities.ForeignAvatars.MatchID(id).ExecuteFirstAsync(token));
 		}

PrivaPub/Api/Mastodon/Controllers/SearchController.cs

@@ -56,7 +56,7 @@ namespace PrivaPub.Api.Mastodon.Controllers
 				{
 					var local = await _localActors.FindByUri(q, token);
 					var foreign = local == default ? (resolve ? await _remoteActors.GetActor(q, refresh: false, token) : default) : default;
-					if (local is { IsFederated: true })
+					if (local is { IsFederated: true, IsCircle: false })
 						results.Accounts.Add(await _mapper.Local(local, false, token));
 					else if (foreign != default)
 						results.Accounts.Add(_mapper.Foreign(foreign));