P5, first batch: summaries stop hiding articles, personas get reachable names, blocks federate

- A remote `summary` is a content warning only on a Note or Question, or when `sensitive` is set. On Articles,
  Events, Videos, Pages and Audio it is an excerpt (WordPress teasers, Mobilizon dates and places, Mbin titles) and
  is now kept as `Post.Excerpt` instead of hiding the post. `Post.ObjectType` records the remote type, and the
  Mastodon API shows a remote non-Note object's title above its body again.
- Persona usernames must match `^[a-z0-9_]+$`, as groups already did; a name outside it was unreachable from
  Mastodon and Misskey.
- `postingRestrictedToMods` is defined in our JSON-LD context (Iceshrimp.NET drops undefined terms).
- `Vary: Accept` on actor and object URLs.
- Owner decision: blocks federate. A block sends `Block`, an unblock `Undo{Block}`; checked live against GoToSocial.
- Owner decision: a persona's and a group's `published`, and the day in new ids, is a random day up to two weeks
  before creation, so personas made the same day no longer share a date. Migration _007 gives existing ones theirs.

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

PrivaPub/Federation/Actors/LocalActorService.cs

@@ -202,7 +202,7 @@ namespace PrivaPub.Federation.Actors
 			ThumbnailURL = avatar.ThumbnailURL,
 			PrivateKeyPem = avatar.PrivateKey,
 			PublicKeyPem = avatar.PublicKey,
-			Published = avatar.CreatedAt,
+			Published = avatar.PublishedOn,
 			Fields = avatar.Fields ?? new Dictionary<string, string>(),
 			ManuallyApprovesFollowers = avatar.Settings?.IsLocked == true,
 			Discoverable = avatar.Settings?.IsDiscoverable != false,
@@ -227,7 +227,7 @@ namespace PrivaPub.Federation.Actors
 			ManuallyApprovesFollowers = group.Kind == GroupKind.Circle || group.ManuallyApprovesMembers,
 			IsCircle = group.Kind == GroupKind.Circle,
 			PostingRestrictedToModerators = group.PostingPolicy == PostingPolicy.Moderators,
-			Published = group.CreationDate,
+			Published = group.PublishedOn,
 			BaseAddress = BaseAddress
 		};
 	}

PrivaPub/Federation/Controllers/PeasantsController.cs

@@ -317,6 +317,8 @@ namespace PrivaPub.Federation.Controllers
 		[NonAction]
 		public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
 		{
+			if (HttpMethods.IsGet(Request.Method))
+				Response.Headers.Vary = "Accept";
 			if (_federation.CurrentValue.SecureMode && HttpMethods.IsGet(Request.Method)
 				&& !string.Equals(context.RouteData.Values["actor"] as string, LocalActorService.InstanceUserName, StringComparison.OrdinalIgnoreCase)
 				&& await _fetches.Requester(Request, HttpContext.RequestAborted) == default)

PrivaPub/Federation/Inbox/Handlers/UpdateHandler.cs

@@ -72,6 +72,7 @@ namespace PrivaPub.Federation.Inbox.Handlers
 
 			post.Title = note.Title;
 			post.SpoilerText = note.SpoilerText;
+			post.Excerpt = note.Excerpt;
 			post.HasContentWarning = note.Sensitive;
 			post.Text = note.ContentHtml;
 			post.ContentHtml = note.ContentHtml;

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -70,8 +70,10 @@ namespace PrivaPub.Federation.Inbox
 				Url = note.Url,
 				ContextURI = note.Context,
 				QuoteURI = note.QuoteUri,
+				ObjectType = note.Type,
 				Title = note.Title,
 				SpoilerText = note.SpoilerText,
+				Excerpt = note.Excerpt,
 				HasContentWarning = note.Sensitive,
 				Text = note.ContentHtml,
 				ContentHtml = note.ContentHtml,

PrivaPub/Federation/Objects/NoteParser.cs

@@ -15,6 +15,7 @@ namespace PrivaPub.Federation.Objects
 		public string ContentHtml { get; init; }
 		public string Title { get; init; }
 		public string SpoilerText { get; init; }
+		public string Excerpt { get; init; }
 		public bool Sensitive { get; init; }
 		public string Language { get; init; }
 		public string Url { get; init; }
@@ -48,6 +49,8 @@ namespace PrivaPub.Federation.Objects
 
 			var (contentHtml, language) = Content(note);
 			var summary = Value(note, "summary");
+			var sensitive = note["sensitive"] is JsonValue flag && flag.TryGetValue<bool>(out var marked) && marked;
+			var summaryWarns = type is "Note" or "Question" || sensitive;
 			return new NoteDocument
 			{
 				Id = id,
@@ -55,9 +58,9 @@ namespace PrivaPub.Federation.Objects
 				AttributedTo = Attribution(note["attributedTo"]),
 				ContentHtml = ContentSanitizer.Html(contentHtml),
 				Title = Plain(Value(note, "name"), 500),
-				SpoilerText = Plain(summary, 500),
-				Sensitive = note["sensitive"] is JsonValue sensitive && sensitive.TryGetValue<bool>(out var s) && s
-					|| !string.IsNullOrWhiteSpace(summary),
+				SpoilerText = summaryWarns ? Plain(summary, 500) : default,
+				Excerpt = summaryWarns ? default : Plain(summary, 1000),
+				Sensitive = sensitive || summaryWarns && !string.IsNullOrWhiteSpace(summary),
 				Language = language,
 				Url = UrlOf(note["url"]) ?? id,
 				InReplyTo = Id(note["inReplyTo"]),

PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

@@ -41,7 +41,9 @@ namespace PrivaPub.Federation.Rendering
 				["schema"] = "http://schema.org#",
 				["PropertyValue"] = "schema:PropertyValue",
 				["value"] = "schema:value",
-				["webfinger"] = "https://purl.archive.org/socialweb/webfinger#webfinger"
+				["webfinger"] = "https://purl.archive.org/socialweb/webfinger#webfinger",
+				["lemmy"] = "https://join-lemmy.org/ns#",
+				["postingRestrictedToMods"] = "lemmy:postingRestrictedToMods"
 			});
 
 		public static string Html(string markdown) =>