Followers and circle members may like, react, vote and downvote

LikeHandler.MaySee let a remote account interact with a followers-only
post only when the post named it in to, cc or its mentions. Our own
followers-only posts are addressed to the followers collection, never to
each follower, and circle posts were not considered at all, so every
like, reaction, downvote and poll vote from a follower on a
followers-only post, and from a member on a circle post, was dropped as
"not-visible". Likes, dislikes, reactions and poll votes now ask
VisibilityPolicy.RemoteCanSee: anyone for public and unlisted posts, an
addressed account for a DM, an accepted follower or an addressed account
for followers-only, a foreign member for a circle post, and never a
server's instance actor (SignedFetchAuthorizer's alias is for refetches
only).

Found by planning the town's multi-server interaction checks (G-0001).

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

PrivaPub/Federation/Inbox/Handlers/DislikeHandler.cs

@@ -1,6 +1,7 @@
 using MongoDB.Driver;
 using MongoDB.Entities;
 
+using PrivaPub.Domain.Privacy;
 using PrivaPub.Models.Social;
 using PrivaPub.Models.User;
 using PrivaPub.StaticServices;
@@ -30,7 +31,7 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			var post = objectUri == default
 				? default
 				: await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && !p.DeletedAt.HasValue && p.ReblogOfPostId == null).ExecuteFirstAsync(token);
-			if (post == default || !LikeHandler.MaySee(post, actor))
+			if (post == default || !await VisibilityPolicy.RemoteCanSee(post, actor, token))
 			{
 				Arrival.Drop(post == default ? "unknown-object" : "not-visible");
 				return;

PrivaPub/Federation/Inbox/Handlers/LikeHandler.cs

@@ -1,6 +1,7 @@
 using MongoDB.Driver;
 using MongoDB.Entities;
 
+using PrivaPub.Domain.Privacy;
 using PrivaPub.Domain.Social;
 using PrivaPub.Models.Post;
 using PrivaPub.Models.Social;
@@ -34,7 +35,7 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			var post = objectUri == default
 				? default
 				: await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && !p.DeletedAt.HasValue && p.ReblogOfPostId == null).ExecuteFirstAsync(token);
-			if (post == default || !MaySee(post, actor))
+			if (post == default || !await VisibilityPolicy.RemoteCanSee(post, actor, token))
 			{
 				Arrival.Drop(post == default ? "unknown-object" : "not-visible");
 				return;
@@ -61,10 +62,5 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			if (!post.IsFederatedCopy)
 				await Notifications.Add(post.GroupUserId, NotificationType.Favourite, actor.ID, actor.ActorURI, post.ID, token);
 		}
-
-		public static bool MaySee(PostEntity post, ForeignAvatar actor) =>
-			post.Visibility is PostVisibility.Public or PostVisibility.Unlisted
-			|| post.Visibility is PostVisibility.FollowersOnly or PostVisibility.Direct
-				&& (post.To.Contains(actor.ActorURI) || post.Cc.Contains(actor.ActorURI) || post.Mentions.Any(m => m.ActorURI == actor.ActorURI));
 	}
 }