A follow of a persona's profile page; an Update under its Create's id

Forte follows a persona by its profile page (/@name, WebFinger's alias) rather than its actor's id: Follow and
Undo{Follow} now find the persona by either (it was a 404). Forte also sends an edit only added to the thread's context
(FEP-171b), under the same activity id as the post's Create: the unwrapping now tells two activities that share an id
apart by what they carry, as the inbox does, so the Update is not taken for a copy.

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

PrivaPub/Federation/Inbox/InboxReceiver.cs

@@ -225,7 +225,7 @@ namespace PrivaPub.Federation.Inbox
 
 		static string HostOf(string uri) => Uri.TryCreate(uri, UriKind.Absolute, out var parsed) ? parsed.Host.ToLowerInvariant() : default;
 
-		static bool CarriesOther(string earlierPayload, JsonNode activity)
+		public static bool CarriesOther(string earlierPayload, JsonNode activity)
 		{
 			if (earlierPayload == default)
 				return false;
@@ -235,7 +235,7 @@ namespace PrivaPub.Federation.Inbox
 		}
 
 		// what an activity carries, short: its type, actor and object
-		static string Digest(JsonNode activity) =>
+		public static string Digest(JsonNode activity) =>
 			Convert.ToHexString(System.Security.Cryptography.SHA256.HashData(System.Text.Encoding.UTF8.GetBytes(
 				$"{Value(activity, "type")}\n{Id(activity["actor"])}\n{activity["object"]?.ToJsonString()}")))[..16].ToLowerInvariant();
 
@@ -252,7 +252,8 @@ namespace PrivaPub.Federation.Inbox
 			switch (type)
 			{
 				case "Follow":
-					var target = await _localActors.FindByUri(Id(inner), token);
+					// (by its actor's id, or the profile page Forte names instead)
+					var target = await _localActors.FindByAddress(Id(inner), token);
 					if (target is not { IsFederated: true } || target.Kind == LocalActorKind.Application)
 						return new(StatusCodes.Status404NotFound, "no such local actor", Reason: "unknown-recipient");
 					break;