One delivery a server; BookWyrm 0.9.3 in the pasture

An activity now goes once to each server, to its shared inbox when it has one, for the accounts a post names, answers
or quotes as for its followers, as Mastodon delivers (a circle post excepted: each member's copy names that member).
BookWyrm took the same post twice when one copy reached its shared inbox and another the named account's inbox at once.
SharedInboxTests checks a reply to a follower's post goes once.

BookWyrm joins the pasture (peers/bookwyrm.sh: its image on the shared Postgres and Redis, gunicorn and a Celery worker,
its user, book and statuses made in its Django shell). scenarios/bookwyrm.sh: follows both ways, a review, a comment and
a quotation reaching alice as BookWyrm's pure posts, her like, boost and reply landing there, her post naming bwuser and
bwuser's like and reply, a deletion, the unfollow and statistics: 20 checks. GoToSocial (64), Mastodon (57) and Misskey
(35) still pass.

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

PrivaPub.Tests/Federation/SharedInboxTests.cs

@@ -0,0 +1,50 @@
+using PrivaPub.Domain.Statuses;
+using PrivaPub.Tests.Support;
+
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Tests.Federation
+{
+	// one delivery a server: a reply to a follower's post goes to its server's shared inbox once, not also to the
+	// follower's own inbox (BookWyrm kept two copies of a post that reached both at once)
+	[Trait("Category", "Integration")]
+	public sealed class SharedInboxTests : 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();
+		}
+
+		[Fact]
+		public async Task A_reply_to_a_followers_post_reaches_its_server_once_through_the_shared_inbox()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var bob = new RemoteActor(_harness.Peer, "bob", sharedInbox: true);
+			await _harness.FollowedBy(alice, bob);
+			var path = $"/notes/{Guid.NewGuid():N}";
+			var noteId = new Uri(bob.Id).GetLeftPart(UriPartial.Authority) + path;
+			_harness.Peer.Serve(path, new JsonObject
+			{
+				["id"] = noteId, ["type"] = "Note", ["attributedTo"] = bob.Id, ["content"] = "<p>a question</p>",
+				["to"] = new JsonArray("https://www.w3.org/ns/activitystreams#Public"), ["published"] = DateTime.UtcNow.ToString("O")
+			}.ToJsonString());
+			var parent = await _harness.RemotePosts.StoreContext(noteId, 0, token);
+
+			var reply = await _harness.Statuses.Publish(alice, new StatusDraft { Text = "an answer", InReplyTo = parent.ID }, token);
+
+			Assert.True(reply.Ok, reply.Error);
+			Assert.Single(await _harness.Outgoing(bob.SharedInbox), a => a["type"]!.GetValue<string>() == "Create");
+			Assert.Empty(await _harness.Outgoing(bob.Id + "/inbox"));
+		}
+	}
+}