A community announces back to its author's own server

Lemmy keeps its user's post in a community pending until the community announces it back. A community hosted here
announced only to its followers, so a post from a server where nobody follows the community stayed pending there; the
author's own server (its shared inbox) now gets the announces too. INTEROP records, confirmed live, why Lemmy refuses
our Flags (an Application reporter, no `to`, an array object). FEDERATION.md's custom emoji line is put back before the
replies paragraph.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub/Federation/Outbox/GroupDistributor.cs

@@ -1,6 +1,7 @@
 using MongoDB.Entities;
 
 using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Objects;
 using PrivaPub.Federation.Rendering;
 using PrivaPub.Models.Federation;
 
@@ -18,6 +19,16 @@ namespace PrivaPub.Federation.Outbox
 	public class GroupDistributor : IGroupDistributor
 	{
 		// so the announce's id resolves (PeasantsController.Grunt); a repeat of the same announce keeps the first
+		// a remote author's server's inbox (its shared one when it has one); none for our own personas
+		static async Task<string[]> AuthorsInbox(JsonObject activity, CancellationToken token)
+		{
+			if (ActivityJson.Id(activity["actor"]) is not { } actorUri)
+				return default;
+			var author = await DB.Default.Find<Models.User.ForeignAvatar>().Match(a => a.ActorURI == actorUri).ExecuteFirstAsync(token);
+			var inbox = string.IsNullOrEmpty(author?.SharedInboxURL) ? author?.InboxURL : author.SharedInboxURL;
+			return string.IsNullOrEmpty(inbox) ? default : new[] { inbox };
+		}
+
 		static async Task Keep(LocalActor group, JsonObject announce, string objectUri, CancellationToken token)
 		{
 			var body = (JsonObject)announce.DeepClone();
@@ -63,16 +74,18 @@ namespace PrivaPub.Federation.Outbox
 				["audience"] = group.Uri,
 				["object"] = embedded
 			};
-			// Every follower, the author's own server included: Lemmy 1.0 keeps its user's post pending until the community
-			// announces it back, and clears that before it answers the echo 400 ("Object is not remote").
-			await _delivery.EnqueueToFollowers(group, announce, token);
+			// Every follower, and the author's own server whether anyone there follows the community or not: Lemmy 1.0 keeps
+			// its user's post pending until the community announces it back, and clears that before it answers the echo 400
+			// ("Object is not remote").
+			var authorsServer = await AuthorsInbox(activity, token);
+			await _delivery.EnqueueToFollowers(group, announce, token, authorsServer);
 			await Keep(group, announce, objectUri, token);
 			// a new post or comment is also boosted as itself: microblogs (Mastodon, Akkoma, Misskey) drop an Announce of an
 			// activity, so without it their members never see what is said in the community; Lemmy answers it 400, harmlessly
 			if (isNewPost && !string.IsNullOrEmpty(objectUri))
 			{
 				var boost = ActivityPubRenderer.Announce(group, objectUri, $"announce-object-{key}");
-				await _delivery.EnqueueToFollowers(group, boost, token);
+				await _delivery.EnqueueToFollowers(group, boost, token, authorsServer);
 				await Keep(group, boost, objectUri, token);
 			}
 		}