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/Federation/Actors/LocalActorService.cs

@@ -65,6 +65,7 @@ namespace PrivaPub.Federation.Actors
 		Task<GoneActor> Gone(string userName, CancellationToken token);
 		Task<LocalActor> FindById(LocalActorKind kind, string id, CancellationToken token);
 		Task<LocalActor> FindByUri(string actorUri, CancellationToken token);
+		Task<LocalActor> FindByAddress(string address, CancellationToken token);
 		Task<LocalActor> GetInstanceActor(CancellationToken token);
 		Task<bool> IsUserNameTaken(string userName, CancellationToken token);
 		Task<bool> TryReserveUserName(string userName, LocalActorKind kind, string ownerId, CancellationToken token);
@@ -153,6 +154,16 @@ namespace PrivaPub.Federation.Actors
 			return FindByUserName(userName, token);
 		}
 
+		// an actor id, or the profile page its document names as `url`: Mbin addresses its private messages to that page
+		public Task<LocalActor> FindByAddress(string address, CancellationToken token)
+		{
+			var profile = $"{BaseAddress}/@";
+			if (string.IsNullOrEmpty(address) || !address.StartsWith(profile, StringComparison.OrdinalIgnoreCase))
+				return FindByUri(address, token);
+			var userName = address[profile.Length..];
+			return userName.Length == 0 || userName.IndexOfAny(['/', '#', '?']) >= 0 ? Task.FromResult<LocalActor>(default) : FindByUserName(userName, token);
+		}
+
 		public async Task<LocalActor> GetInstanceActor(CancellationToken token)
 		{
 			var instance = _instanceActor ??= await LoadInstanceActor(token);