A remote account's Block of a persona is enforced

Inbound Block was dropped as an unknown type (the pasture's last
Mastodon expected failure, G-0002). Now, as Mastodon does it: the
follows between the blocker and the persona end here too (nothing is
sent back; the blocker already ended its side), the blocker's posts and
notifications are hidden from the persona and kept out of its home, the
persona's posts are no longer addressed to the blocker by mention or
reply, and the relationship says blocked_by. Undo{Block} lifts it. The
block is kept in BlockedBy, unique per persona and blocker.

The Mastodon scenario checks blocked_by instead of expecting a failure.

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

PrivaPub.Tests/Federation/InboundBlockTests.cs

@@ -0,0 +1,77 @@
+using MongoDB.Entities;
+
+using PrivaPub.Domain.Relationships;
+using PrivaPub.Models.Federation;
+using PrivaPub.Models.Social;
+using PrivaPub.Tests.Support;
+
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Tests.Federation
+{
+	// A remote account's Block of a persona, as Mastodon sends it (the pasture's last Mastodon expected failure, G-0002)
+	[Trait("Category", "Integration")]
+	public sealed class InboundBlockTests : IAsyncLifetime
+	{
+		Harness _harness;
+
+		public async ValueTask InitializeAsync()
+		{
+			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
+			_harness = await Harness.Start();
+		}
+
+		public async ValueTask DisposeAsync()
+		{
+			if (_harness != default)
+				await _harness.DisposeAsync();
+		}
+
+		static string Origin(RemoteActor actor) => new Uri(actor.Id).GetLeftPart(UriPartial.Authority);
+
+		[Fact]
+		public async Task A_block_ends_the_follows_both_ways_hides_the_blocker_and_its_undo_lifts_it()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var carol = new RemoteActor(_harness.Peer, "carol");
+			await _harness.FollowedBy(alice, carol);
+			await DB.Default.SaveAsync(new Following { AvatarId = alice.Id, TargetActorURI = carol.Id, State = FollowState.Accepted }, token);
+			var block = new JsonObject
+			{
+				["id"] = $"{Origin(carol)}/blocks/{Guid.NewGuid():N}", ["type"] = "Block", ["actor"] = carol.Id, ["object"] = alice.Uri
+			};
+
+			await _harness.Deliver(carol, $"/peasants/{alice.UserName}/mouth", block);
+
+			Assert.True(await DB.Default.Find<BlockedBy>().Match(b => b.AvatarId == alice.Id && b.ActorURI == carol.Id).ExecuteAnyAsync(token));
+			Assert.False(await DB.Default.Find<Follower>().Match(f => f.LocalActorId == alice.Id && f.ActorURI == carol.Id).ExecuteAnyAsync(token));
+			Assert.False(await DB.Default.Find<Following>().Match(f => f.AvatarId == alice.Id && f.TargetActorURI == carol.Id).ExecuteAnyAsync(token));
+			Assert.Contains(carol.Id, await Hidden.AuthorsHiddenFrom(alice.Id, new[] { carol.Id }, forNotifications: false, token));
+			Assert.Contains(alice.Id, await Hidden.RecipientsHiding(new[] { alice.Id }, carol.Id, token));
+
+			await _harness.Deliver(carol, $"/peasants/{alice.UserName}/mouth", new JsonObject
+			{
+				["id"] = $"{Origin(carol)}/undos/{Guid.NewGuid():N}", ["type"] = "Undo", ["actor"] = carol.Id, ["object"] = block
+			});
+
+			Assert.False(await DB.Default.Find<BlockedBy>().Match(b => b.AvatarId == alice.Id && b.ActorURI == carol.Id).ExecuteAnyAsync(token));
+			Assert.Empty(await Hidden.AuthorsHiddenFrom(alice.Id, new[] { carol.Id }, forNotifications: false, token));
+		}
+
+		[Fact]
+		public async Task A_block_of_someone_who_is_not_ours_is_dropped()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var carol = new RemoteActor(_harness.Peer, "carol");
+
+			await _harness.Deliver(carol, "/human-centipede", new JsonObject
+			{
+				["id"] = $"{Origin(carol)}/blocks/{Guid.NewGuid():N}", ["type"] = "Block", ["actor"] = carol.Id,
+				["object"] = $"{Origin(carol)}/users/somebody-else"
+			});
+
+			Assert.False(await DB.Default.Find<BlockedBy>().Match(b => b.ActorURI == carol.Id).ExecuteAnyAsync(token));
+		}
+	}
+}

PrivaPub.Tests/Support/Harness.cs

@@ -67,7 +67,8 @@ namespace PrivaPub.Tests.Support
 				new CreateHandler(Db, Local, Remote, Delivery, new NoBlocks(), Fanout, RemotePosts, Groups, Records, Polls, new NoPreviews(), Quotes),
 				new DeleteHandler(Db, Local, Remote, Delivery, Groups, Quotes),
 				new UpdateHandler(Db, Local, Remote, Groups, Records, Quotes),
-				new FlagHandler(Db, Local)
+				new FlagHandler(Db, Local),
+				new BlockHandler(Db, Local)
 			};
 			Processor = new InboxProcessor(Remote, Handlers, NullLogger<InboxProcessor>.Instance, Ledger);
 			Follows = new FollowService(Db, Local, Remote, Delivery, new KeyLocalizer<GenericRes>(), NullLogger<FollowService>.Instance);