A follow request sent again carries a new id

Lemmy keeps the ids of the activities it received and never answers one again, so resending the same Follow could not
heal a follow whose Accept it lost: the village's community follow stayed pending through two resends. Each resend is
now the same follow under its own id (<follow id>-again-<n>), and an Accept naming any of them answers the follow;
the Undo still embeds the follow, so servers match it by its actor and object. Sent this way, the stuck follow was
accepted at once.

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

PrivaPub/Domain/Social/FollowService.cs

@@ -298,7 +298,10 @@ namespace PrivaPub.Domain.Social
 				var inbox = following.TargetInboxURL ?? (await _remoteActors.GetActor(following.TargetActorURI, refresh: false, token))?.InboxURL;
 				if (follower != default && !string.IsNullOrEmpty(inbox))
 				{
-					await _delivery.Enqueue(follower, new[] { inbox }, FollowActivity(follower, following), token,
+					// under a new id each time: Lemmy keeps the ids it received and never answers one again
+					var again = FollowActivity(follower, following);
+					again["id"] = AgainId(following.FollowActivityURI, following.Resent + 1);
+					await _delivery.Enqueue(follower, new[] { inbox }, again, token,
 						again: "resend-" + now.ToString("yyyyMMddHHmm", System.Globalization.CultureInfo.InvariantCulture));
 					sent++;
 				}
@@ -308,6 +311,11 @@ namespace PrivaPub.Domain.Social
 			return sent;
 		}
 
+		// a follow sent again is the same follow under a new id, which an answer may name (AcceptHandler.FindFollowing)
+		public const string Again = "-again-";
+
+		public static string AgainId(string followActivityUri, int resend) => $"{followActivityUri}{Again}{resend}";
+
 		static JsonObject FollowActivity(LocalActor follower, Following following) => new()
 		{
 			["@context"] = ActivityPubRenderer.ActivityStreams,