Load: a flood of fake servers; unique-key lookups no longer scan

tools/pasture/flood/flood.cs answers as twenty fake servers (flood1..20.test)
and sends signed Creates, Likes and Follows at a set rate; load.sh measures
the answers, the queue's wait and processing times, its drain and a persona's
home timeline meanwhile (docs/LOAD.md has the method and the runs).

What the runs found:
- Every unique index was partial on $type: "string", which MongoDB never uses
  for an equality lookup, so every post by ObjectURI, actor by ActorURI,
  deleted object, domain block, remote instance and the rest was a
  collection scan (280 ms a post lookup at 30 000 posts). They are partial on
  $gt: "" now, which an equality on a string implies; MongoDB.Entities
  rebuilds them in place at the next start.
- Two inbox workers capped intake near 110 activities a second:
  Federation:InboxConcurrency and DeliveryConcurrency (default 8) set them.
- The indexes the plan listed as missing: a post's boosts and replies, a
  persona's boosts, who follows an actor, timeline rows by author, a post's
  likes and pins.

At 300 activities a second (200 let through, the rest 429 by the per-origin
limit) the queue wait went from 29 s to 6 ms at p50; with the limits lifted
PrivaPub processes about 900 a second, each in under 10 ms, and the home
timeline stays under 20 ms.

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

PrivaPub/Federation/Inbox/InboxProcessor.cs

@@ -28,9 +28,13 @@ namespace PrivaPub.Federation.Inbox
 		readonly IInteractionLedger _ledger;
 		readonly ILocalActorService _localActors;
 
+		readonly int _concurrency;
+
 		public InboxProcessor(IRemoteActorService remoteActors, IEnumerable<IActivityHandler> handlers, ILogger<InboxProcessor> logger,
-			IInteractionLedger ledger = default, ILocalActorService localActors = default)
+			IInteractionLedger ledger = default, ILocalActorService localActors = default,
+			Microsoft.Extensions.Options.IOptions<Infrastructure.Http.FederationOptions> federation = default)
 		{
+			_concurrency = Math.Max(1, federation?.Value.InboxConcurrency ?? 8);
 			_localActors = localActors;
 			_remoteActors = remoteActors;
 			_handlers = handlers.ToDictionary(h => h.Type, StringComparer.Ordinal);
@@ -39,7 +43,7 @@ namespace PrivaPub.Federation.Inbox
 		}
 
 		public JobKind Kind => JobKind.ProcessInbox;
-		public int Concurrency => 2;
+		public int Concurrency => _concurrency;
 		public int MaxAttempts => 8;
 		public int PerHostLimit => 2;