Moves carry follows over; first DMs to Lemmy 0.19 and Mbin go as ChatMessage

Two owner decisions of 2026-10-05, both recorded in ROADMAP:
- After a verified Move the personas following the old account follow the new one, in the same lists, and a mute or
  block of the old account carries over, as Mastodon does it.
- A direct message to one account on a server whose NodeInfo names Lemmy before 1.0 or Mbin goes as a ChatMessage,
  the one place PrivaPub decides by a server's software (invariant 17). G-0008 is closed.

Mbin addresses its private messages to the recipient's profile page, so a Create addressed to a persona's /@name now
reaches the persona. Checked live: moves 8/8, Lemmy 0.19 30/30, Mbin 26/26 with messages both ways. The software
theory runs alone, since every test's peer shares 127.0.0.1.

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

PrivaPub/Domain/Statuses/StatusService.cs

@@ -248,9 +248,10 @@ namespace PrivaPub.Domain.Statuses
 					.Concat(post.Mentions)
 					.DistinctBy(m => m.ActorURI)
 					.ToList();
-				// to someone who writes to us as ChatMessages (Lemmy 0.19 and Mbin take a private message no other way), in kind
-				post.AsChatMessage = recipients is [{ LocalId: null } recipient]
-					&& await _dbEntities.Posts.Match(p => p.ActorURI == recipient.Uri && p.IsFederatedCopy && p.ObjectType == "ChatMessage").ExecuteAnyAsync(token);
+				// to one account elsewhere, as a ChatMessage when it writes to us that way, or when its server takes a private message
+				// no other way (Lemmy 0.19 and Mbin)
+				post.AsChatMessage = recipients is [{ LocalId: null } recipient] && (await TakesOnlyChatMessages(recipient.Uri, token)
+					|| await _dbEntities.Posts.Match(p => p.ActorURI == recipient.Uri && p.IsFederatedCopy && p.ObjectType == "ChatMessage").ExecuteAnyAsync(token));
 				var note = ActivityPubRenderer.DirectNote(post, author, recipients.Select(r => (r.Uri, r.Handle)).ToList(), dmGroup.ConversationURI);
 				create = ActivityPubRenderer.Create(author, note, $"create-{post.ID}");
 				post.To = Strings(note["to"]);
@@ -547,6 +548,23 @@ namespace PrivaPub.Domain.Statuses
 
 		sealed record Recipient(string Uri, string Handle, string LocalId, string ForeignId, string Inbox);
 
+		// The one place PrivaPub decides by a server's software (owner decision 2026-10-05, G-0008): Lemmy before 1.0 and
+		// Mbin answer a direct Note 400 or drop it, and their actors say nothing of what they take, so the first message to
+		// one of their accounts goes as a ChatMessage, as NodeInfo names them
+		async Task<bool> TakesOnlyChatMessages(string actorUri, CancellationToken token)
+		{
+			if (!Uri.TryCreate(actorUri, UriKind.Absolute, out var uri))
+				return false;
+			var host = uri.Host;
+			var instance = await DB.Default.Find<Models.Jobs.RemoteInstance>().Match(i => i.Host == host).ExecuteFirstAsync(token);
+			return instance?.Software?.ToLowerInvariant() switch
+			{
+				"mbin" => true,
+				"lemmy" => instance.SoftwareVersion is { } version && version.StartsWith("0.", StringComparison.Ordinal),
+				_ => false
+			};
+		}
+
 		sealed record ConversationResult(DmGroup Group, IReadOnlyList<Recipient> Recipients, int Status = StatusCodes.Status200OK, string Error = default)
 		{
 			public bool Ok => Error == default;