The inbox answers once it has verified, and processes from the job queue

InboxService is split the way the roadmap lays out Federation/Inbox:
- InboxReceiver reads and verifies the request exactly as before, runs
  the checks that need no fetch (the activity id's origin, a Follow of a
  missing or local-only actor, an Undo of someone else's activity, an
  embedded object attributed to someone else), queues a ProcessInbox job
  and answers 202. The job's dedupe key is the activity id, so a peer that
  delivers the same activity twice is processed once.
- InboxProcessor (two at a time, eight attempts) loads the verified actor
  and hands the activity to the handler for its type.
- Handlers/{Follow,Undo,Create,Delete,Update}Handler are the old methods,
  unchanged except that they no longer produce status codes; the JSON
  helpers live in Objects/ActivityJson and the group membership helpers in
  Inbox/ForeignMembers.

A slow fetch of an object or a remote actor now delays the job, not the
sender's HTTP request.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Federation/Objects/ActivityJson.cs

@@ -0,0 +1,39 @@
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Federation.Objects
+{
+	public static class ActivityJson
+	{
+		public static string Id(JsonNode node) => node switch
+		{
+			JsonValue value when value.TryGetValue<string>(out var text) => text,
+			JsonObject obj => Value(obj, "id") ?? Value(obj, "href"),
+			JsonArray array => array.Select(Id).FirstOrDefault(i => i != default),
+			_ => default
+		};
+
+		public static string Value(JsonNode node, string property) =>
+			node is JsonObject obj && obj[property] is JsonValue value && value.TryGetValue<string>(out var text) ? text : default;
+
+		public static IEnumerable<string> Addresses(JsonNode node)
+		{
+			foreach (var field in new[] { "to", "cc", "bto", "bcc", "audience" })
+			{
+				switch (node[field])
+				{
+					case JsonArray array:
+						foreach (var item in array)
+						{
+							var id = Id(item);
+							if (id != default)
+								yield return id;
+						}
+						break;
+					case JsonNode single when Id(single) is { } id:
+						yield return id;
+						break;
+				}
+			}
+		}
+	}
+}