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/Support/Harness.cs

@@ -34,6 +34,8 @@ namespace PrivaPub.Tests.Support
 		public const string Host = "privapub.test";
 		public const string Base = "https://" + Host;
 
+		readonly DateTime _started = Millisecond(DateTime.UtcNow);
+
 		Harness(Peer peer)
 		{
 			Peer = peer;
@@ -136,13 +138,15 @@ namespace PrivaPub.Tests.Support
 		}
 
 		public async Task<List<JsonObject>> Outgoing(string inbox) =>
-			(await DB.Default.Find<Job>().Match(j => j.Kind == JobKind.Deliver).ExecuteAsync())
+			(await DB.Default.Find<Job>().Match(j => j.Kind == JobKind.Deliver && j.CreatedAt >= _started).ExecuteAsync())
 				.Select(j => JsonSerializer.Deserialize<DeliveryPayload>(j.Payload))
 				.Where(p => p.Inbox == inbox)
 				.Select(p => JsonNode.Parse(p.Body)!.AsObject())
 				.ToList();
 
 		public async ValueTask DisposeAsync() => await Peer.DisposeAsync();
+
+		static DateTime Millisecond(DateTime time) => new(time.Ticks - time.Ticks % TimeSpan.TicksPerMillisecond, DateTimeKind.Utc);
 	}
 
 	public sealed class KeyLocalizer<T> : IStringLocalizer<T>