Personas a remote post is addressed to see it, named or not

A remote post decided who here may see it by its Mention tags alone. A
followers-only post addressed in to or cc to a persona without naming
it (Akkoma's to[], or a GoToSocial edit that took the @name out while
the post stayed addressed to the persona) was hidden from that persona.
Such personas are now kept as silent mentions, as Mastodon does: they
see the post and it reaches their home, and no list shows them as
mentioned. An edit never narrows who a post was for.

The GoToSocial note that showed it is the first captured fixture
(Fixtures/gotosocial), and parses with its lone tag, to and cc.

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

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -55,15 +55,33 @@ namespace PrivaPub.Federation.Inbox
 			_queue = queue;
 		}
 
-		public async Task<PostEntity> Build(NoteDocument note, ForeignAvatar author, PostVisibility visibility, IReadOnlyList<string> to,
-			IReadOnlyList<string> cc, PostEntity parent, CancellationToken token)
+		// The accounts a remote post names (its Mention tags), plus our personas it is addressed to without naming them: Mastodon
+		// keeps those as silent mentions, and Akkoma's to[], or an edit that dropped the @name, address someone that way. A
+		// silent mention lets the persona see the post and puts it in its home, and is never shown as a mention.
+		public static async Task<List<PostMention>> Mentions(NoteDocument note, IEnumerable<string> addressed, ILocalActorService localActors,
+			CancellationToken token)
 		{
 			var mentions = new List<PostMention>();
 			foreach (var mention in note.Mentions)
 			{
-				var local = await _localActors.FindByUri(mention.ActorURI, token);
+				var local = await localActors.FindByUri(mention.ActorURI, token);
 				mentions.Add(new PostMention { ActorURI = mention.ActorURI, Handle = mention.Handle, IsLocal = local != default, AccountId = local?.Id });
 			}
+			foreach (var uri in addressed.Where(a => !string.IsNullOrEmpty(a) && !Addressing.IsPublic(a)).Distinct(StringComparer.Ordinal))
+			{
+				if (mentions.Any(m => m.ActorURI == uri))
+					continue;
+				var local = await localActors.FindByUri(uri, token);
+				if (local is { Kind: LocalActorKind.Person })
+					mentions.Add(new PostMention { ActorURI = uri, Handle = "@" + local.Handle, IsLocal = true, AccountId = local.Id, Silent = true });
+			}
+			return mentions;
+		}
+
+		public async Task<PostEntity> Build(NoteDocument note, ForeignAvatar author, PostVisibility visibility, IReadOnlyList<string> to,
+			IReadOnlyList<string> cc, PostEntity parent, CancellationToken token)
+		{
+			var mentions = await Mentions(note, to.Concat(cc), _localActors, token);
 
 			return new PostEntity
 			{