A community's vote on our reply counts, followed or not

Lemmy sends a vote to the community alone, which relays it to the post's
server. A persona's reply in a thread of a community nobody here follows
lost its Lemmy upvotes: the relay was dropped as "not followed". Such a
relay is now taken when the vote (or its undo) is on one of our posts in a
thread rooted in that community; from any other unfollowed group it is
still dropped. For that, a post keeps the community its `audience` names
(FEP-1b12) however it arrived, fetched for a thread as well as announced.

Found by the town's village (p191: 1 like counted of 2).

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

PrivaPub/Federation/Inbox/Handlers/AnnounceHandler.cs

@@ -143,7 +143,8 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		{
 			Arrival.About(Value(inner, "type"));
 			if (group.AvatarType != AvatarType.Group
-				|| !await _dbEntities.Followings.Match(f => f.TargetActorURI == group.ActorURI && f.State == FollowState.Accepted).ExecuteAnyAsync(token))
+				|| !await _dbEntities.Followings.Match(f => f.TargetActorURI == group.ActorURI && f.State == FollowState.Accepted).ExecuteAnyAsync(token)
+					&& !await OurPostInItsThread(inner, group, token))
 			{
 				Arrival.Drop("not-followed");
 				return;
@@ -230,6 +231,28 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			}
 		}
 
+		// A vote (or its undoing) on one of our posts in a thread the community holds: the community relays it to the post's
+		// server whether or not anyone here follows the community (Lemmy sends a vote to the community alone)
+		async Task<bool> OurPostInItsThread(JsonNode inner, ForeignAvatar group, CancellationToken token)
+		{
+			var target = Value(inner, "type") switch
+			{
+				"Like" or "Dislike" => Id(inner["object"]),
+				"Undo" when (inner["object"] as JsonObject)?["type"]?.GetValue<string>() is "Like" or "Dislike" => Id(inner["object"]?["object"]),
+				_ => default
+			};
+			var post = target == default
+				? default
+				: await _dbEntities.Posts.Match(p => p.ObjectURI == target && !p.IsFederatedCopy && !p.DeletedAt.HasValue).ExecuteFirstAsync(token);
+			for (var depth = 0; post != default && depth < RemotePosts.MaxDepth; depth++)
+			{
+				if (post.AudienceURI == group.ActorURI)
+					return true;
+				post = string.IsNullOrEmpty(post.AnsweringToPostId) ? default : await _dbEntities.Posts.MatchID(post.AnsweringToPostId).ExecuteFirstAsync(token);
+			}
+			return false;
+		}
+
 		// A community's moderators lock one of its posts, or unlock it: no more replies, ours included. The community vouches
 		// for what is done to its own posts.
 		async Task Lock(string objectUri, ForeignAvatar group, bool locked, CancellationToken token)

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -94,6 +94,11 @@ namespace PrivaPub.Federation.Inbox
 				Cc = cc.ToList(),
 				Url = note.Url,
 				ContextURI = note.Context,
+				// the community it lives in (FEP-1b12), as the post itself names it: a post fetched for a thread knows its
+				// community as well as one its community announced
+				AudienceURI = note.Audience != default && note.Audience != author.ActorURI && !note.Audience.EndsWith("/followers", StringComparison.Ordinal)
+					? note.Audience
+					: default,
 				QuoteURI = note.QuoteUri,
 				ObjectType = note.Type,
 				Title = note.Title,