T1: tests stop sharing state they don't own

- JobQueue takes an optional scope, so a test's worker leases and reaps only its own jobs.
- The dead-host delivery test runs alone (Exclusive), on its own jobs, and cleans up the
  breaker rows it trips; the breaker has tests of its own on unique hosts.
- Index and migration tests run alone: they drop indexes and rewrite every post.
- DomainBlocks.Load replaces reflection and a database-wide block in tests.
- Harness.Outgoing sees only deliveries queued since the harness started: Peer ports are
  reused within a run, which made the circle test flaky.
- Two pure-logic tests leave Mongo-gated classes, so CI runs them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

PrivaPub.Tests/Infrastructure/DeliveryWorkerTests.cs

@@ -0,0 +1,95 @@
+using Microsoft.Extensions.Caching.Memory;
+using Microsoft.Extensions.Logging.Abstractions;
+
+using MongoDB.Entities;
+
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Outbox;
+using PrivaPub.Infrastructure.Jobs;
+using PrivaPub.Models;
+using PrivaPub.Models.Jobs;
+using PrivaPub.Models.User;
+using PrivaPub.StaticServices;
+using PrivaPub.Tests.Support;
+
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Tests.Infrastructure
+{
+	[Xunit.Collection(nameof(Exclusive))]
+	[Trait("Category", "Integration")]
+	public sealed class DeliveryWorkerTests : IAsyncLifetime
+	{
+		static readonly string[] PeerHosts = { "localhost", "127.0.0.1" };
+
+		Peer _peer;
+
+		public async ValueTask InitializeAsync()
+		{
+			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
+			_peer = await Peer.Start();
+			await DB.Default.DeleteAsync<RemoteInstance>(i => PeerHosts.Contains(i.Host));
+		}
+
+		public async ValueTask DisposeAsync()
+		{
+			if (_peer == default)
+				return;
+			await _peer.DisposeAsync();
+			await DB.Default.DeleteAsync<RemoteInstance>(i => PeerHosts.Contains(i.Host));
+		}
+
+		[Fact]
+		public async Task A_dead_host_does_not_hold_up_deliveries_to_live_ones()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (privateKey, publicKey) = Keys.NewKeyPair();
+			var avatar = new Avatar { UserName = $"sender{Guid.NewGuid():N}"[..20], PrivateKey = privateKey, PublicKey = publicKey };
+			await DB.Default.SaveAsync(avatar, token);
+			var local = new LocalActorService(new DbEntities(), new StaticOptions<AppConfiguration>(new AppConfiguration { BackendBaseAddress = "https://privapub.test" }));
+			var sender = local.FromAvatar(avatar);
+			var run = $"https://privapub.test/a/{Guid.NewGuid():N}/";
+			var queue = new JobQueue(j => j.DedupeKey.StartsWith(run));
+			var delivery = new DeliveryService(new DbEntities(), queue);
+			_peer.Answer("/dead/inbox", 503, TimeSpan.FromMilliseconds(300));
+			_peer.Answer("/live/inbox", 202);
+
+			var deadInboxes = Enumerable.Range(0, 60).Select(i => $"{_peer.B}/dead/inbox?{i}");
+			await delivery.Enqueue(sender, deadInboxes, new JsonObject { ["id"] = run + "dead", ["type"] = "Create" }, token);
+			await delivery.Enqueue(sender, new[] { $"{_peer.A}/live/inbox" }, new JsonObject { ["id"] = run + "live", ["type"] = "Create" }, token);
+
+			var handler = new DeliveryJobHandler(local, Peer.Http(), new HostCircuitBreaker(new MemoryCache(new MemoryCacheOptions())), NullLogger<DeliveryJobHandler>.Instance);
+			using var worker = new JobWorker(queue, new IJobHandler[] { handler }, NullLogger<JobWorker>.Instance);
+			await worker.StartAsync(token);
+			try
+			{
+				await Until(() => Task.FromResult(_peer.Requests.Any(r => r.Path == "/live/inbox")), token);
+				var deadSoFar = _peer.Requests.Count(r => r.Path == "/dead/inbox");
+				var live = Assert.Single(_peer.Requests, r => r.Path == "/live/inbox");
+				Assert.Contains($"keyId=\"{sender.KeyId}\"", live.Signature);
+				Assert.True(deadSoFar < 30, $"{deadSoFar} dead deliveries were tried before the live one");
+
+				await Until(() => DB.Default.Find<Job>().Match(j => j.DedupeKey.StartsWith(run + "dead") && j.State == JobState.Pending && j.Attempts > 0).ExecuteAnyAsync(token), token);
+			}
+			finally
+			{
+				await worker.StopAsync(CancellationToken.None);
+			}
+
+			var retried = await DB.Default.Find<Job>().Match(j => j.DedupeKey.StartsWith(run + "dead") && j.Attempts > 0 && j.State == JobState.Pending).ExecuteFirstAsync(token);
+			Assert.Equal("503", retried.LastError?.Split(' ')[0]);
+			Assert.True(retried.RunAt > DateTime.UtcNow);
+			Assert.True((await DB.Default.Find<RemoteInstance>().Match(i => i.Host == "localhost").ExecuteFirstAsync(token))?.ConsecutiveFailures > 0);
+		}
+
+		static async Task Until(Func<Task<bool>> condition, CancellationToken token)
+		{
+			var deadline = DateTime.UtcNow.AddSeconds(30);
+			while (!await condition())
+			{
+				Assert.True(DateTime.UtcNow < deadline, "timed out");
+				await Task.Delay(50, token);
+			}
+		}
+	}
+}