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.Tests/Federation/InboundRoutingTests.cs

@@ -2,6 +2,7 @@ using MongoDB.Entities;
 
 using PrivaPub.ClientModels.Post;
 using PrivaPub.Federation.Objects;
+using PrivaPub.Models.Group;
 using PrivaPub.Models.Post;
 using PrivaPub.Tests.Support;
 
@@ -106,6 +107,32 @@ namespace PrivaPub.Tests.Federation
 			Assert.NotNull(message.ConversationId);
 		}
 
+		// Mbin addresses its private messages to the recipient's profile page (its `url`), not to the actor
+		[Fact]
+		public async Task A_chat_message_addressed_to_a_personas_profile_page_reaches_the_persona()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var mbin = new RemoteActor(_harness.Peer, "mbuser");
+			var messageId = NewId(mbin, "f/object");
+
+			await _harness.Deliver(mbin, "/human-centipede", new JsonObject
+			{
+				["id"] = NewId(mbin, "f/object"), ["type"] = "Create", ["actor"] = mbin.Id, ["to"] = new JsonArray(alice.HtmlUrl), ["cc"] = new JsonArray(),
+				["object"] = new JsonObject
+				{
+					["id"] = messageId, ["type"] = "ChatMessage", ["attributedTo"] = mbin.Id, ["to"] = new JsonArray(alice.HtmlUrl), ["cc"] = new JsonArray(),
+					["content"] = "<p>an answer</p>", ["mediaType"] = "text/html", ["published"] = DateTime.UtcNow.ToString("O")
+				}
+			});
+
+			var message = await DB.Default.Find<Post>().Match(p => p.ObjectURI == messageId).ExecuteFirstAsync(token);
+			Assert.NotNull(message);
+			Assert.Equal(PostVisibility.Direct, message.Visibility);
+			var conversation = await DB.Default.Find<DmGroup>().OneAsync(message.ConversationId, token);
+			Assert.Equal(new[] { alice.Id, mbin.Id }.Order(StringComparer.Ordinal), conversation.Members.Select(m => m.AvatarId).Order(StringComparer.Ordinal));
+		}
+
 		// Lemmy 0.19 and Mbin take a private message only as a ChatMessage: someone who writes to us that way is answered in
 		// kind, anyone else with a Note
 		[Fact]