A direct message answers in the form its recipient writes in

Lemmy 0.19 (most of the threadiverse) and Mbin take a private message only
as a ChatMessage and refuse a direct Note. A direct message to one account
elsewhere that writes to us as ChatMessages now goes out as one: to it
alone, without a mention in its text, kept on the post (Post.AsChatMessage)
so the served copy and an edit match. No software name decides it.

Live against Lemmy 0.19: alice's answer to lemmyuser's private message and
another persona's message to lemmyuser arrive (29 checks). A first message
to an account that never wrote to anyone here is still a Note, which they
refuse; G-0008 keeps that open for the owner.

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

PrivaPub/Domain/Statuses/StatusService.cs

@@ -248,6 +248,9 @@ 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);
 				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"]);