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/Infrastructure/Jobs/JobQueue.cs

@@ -4,6 +4,7 @@ using MongoDB.Entities;
 using PrivaPub.Models.Jobs;
 
 using System.Collections.Concurrent;
+using System.Linq.Expressions;
 
 namespace PrivaPub.Infrastructure.Jobs
 {
@@ -39,6 +40,13 @@ namespace PrivaPub.Infrastructure.Jobs
 
 		readonly string _owner = $"{Environment.MachineName}:{Environment.ProcessId}";
 		readonly ConcurrentDictionary<JobKind, SemaphoreSlim> _signals = new();
+		readonly FilterDefinition<Job> _scope = Builders<Job>.Filter.Empty;
+
+		public JobQueue()
+		{
+		}
+
+		public JobQueue(Expression<Func<Job, bool>> scope) => _scope = Builders<Job>.Filter.Where(scope);
 
 		public async Task<bool> Enqueue(JobKind kind, string payload, string host, string dedupeKey, CancellationToken token) =>
 			await EnqueueMany(new[] { new Job { Kind = kind, Payload = payload, Host = host, DedupeKey = dedupeKey } }, token) == 1;
@@ -66,7 +74,7 @@ namespace PrivaPub.Infrastructure.Jobs
 			var now = DateTime.UtcNow;
 			var busy = busyHosts?.ToList() ?? new List<string>();
 			return await DB.Default.UpdateAndGet<Job>()
-				.Match(j => j.Kind == kind && j.State == JobState.Pending && j.RunAt <= now && !busy.Contains(j.Host))
+				.Match(f => f.Where(j => j.Kind == kind && j.State == JobState.Pending && j.RunAt <= now && !busy.Contains(j.Host)) & _scope)
 				.Modify(j => j.State, JobState.Running)
 				.Modify(j => j.LeasedUntil, now + LeaseTime)
 				.Modify(j => j.LeaseOwner, _owner)
@@ -106,7 +114,7 @@ namespace PrivaPub.Infrastructure.Jobs
 		{
 			var now = DateTime.UtcNow;
 			var result = await DB.Default.Update<Job>()
-				.Match(j => j.State == JobState.Running && j.LeasedUntil < now)
+				.Match(f => f.Where(j => j.State == JobState.Running && j.LeasedUntil < now) & _scope)
 				.Modify(j => j.State, JobState.Pending)
 				.Modify(j => j.RunAt, now)
 				.Modify(j => j.LeasedUntil, null)