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.Tests/Federation/InboxGapTests.cs

@@ -209,6 +209,36 @@ namespace PrivaPub.Tests.Federation
 			Assert.False(await DB.Default.Find<Favourite>().Match(f => f.PostId == post.ID).ExecuteAnyAsync(token));
 		}
 
+		// Lemmy sends a vote to the community alone: a vote on our reply in a thread of a community nobody here follows still
+		// reaches us through it, and only through that community (found by the town's village)
+		[Fact]
+		public async Task A_vote_on_our_reply_in_an_unfollowed_communitys_thread_counts_through_that_community_only()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var community = new RemoteActor(_harness.Peer, "cats", type: "Group");
+			var other = new RemoteActor(_harness.Peer, "dogs", type: "Group");
+			var poster = new RemoteActor(_harness.Peer, "poster");
+			var voter = new RemoteActor(_harness.Peer, "voter");
+			var page = PublicNote(poster, "<p>a thread</p>", community.Id);
+			page["type"] = "Page";
+			page["name"] = "a thread";
+			page["audience"] = community.Id;
+			_harness.Peer.Serve(new Uri(IdOf(page)).AbsolutePath, page.ToJsonString());
+			var root = await _harness.RemotePosts.StoreContext(IdOf(page), 0, token);
+			Assert.Equal(community.Id, root.AudienceURI);
+			var reply = (await _harness.Statuses.Publish(alice, new StatusDraft { Text = "my answer", InReplyTo = root.ID }, token)).Post;
+			var like = new JsonObject { ["id"] = NewId(voter, "likes"), ["type"] = "Like", ["actor"] = voter.Id, ["object"] = reply.ObjectURI };
+
+			await _harness.Deliver(other, "/human-centipede", Activity(other, "Announce", like));
+			Assert.Equal(("dropped", "not-followed"), (Processed("Announce").Outcome, Processed("Announce").Reason));
+			await _harness.Deliver(community, "/human-centipede", Activity(community, "Announce", like));
+			Assert.Equal("accepted", Processed("Announce").Outcome);
+			Assert.Equal(1, (await DB.Default.Find<Post>().OneAsync(reply.ID, token)).FavouritesCount);
+			await _harness.Deliver(community, "/human-centipede", Activity(community, "Announce", Activity(voter, "Undo", like)));
+			Assert.Equal(0, (await DB.Default.Find<Post>().OneAsync(reply.ID, token)).FavouritesCount);
+		}
+
 		// Lemmy's moderators lock a community's post and ban members, and the community relays both inside its Announce
 		// (G-0006): a locked post takes no reply, a banned persona posts nothing there, until the Undo
 		[Fact]