M6: provenance fixes, stored features, community edits that are real edits

- A fetched ObjectRecord no longer wears the signature, key, signed headers and @context
  of the activity that caused the fetch, and its ReceivedAt is the fetch's own time. Its
  activity fields now name the trigger. Provenance answers signature null and
  fetchedBy "instance-actor". Migration _008 clears the old fetched records.
- ObjectRecords store their ObjectFeatures extensions and context namespaces (migration
  _009 fills older records in batches), so statistics can count them. Provenance reads the
  stored lists.
- ForeignAvatar.Features records what an actor document uses (ActorFeatures): featured,
  shared inbox, FEP-521a, FEP-8b32, identity proofs, Misskey fields, indexable,
  undiscoverable, locked, key size, and more.
- RemoteEdits.Apply and RemoteDeletes.Remove are shared by the Update, Delete and Announce
  handlers. A community-wrapped Update is now an edit only when newer, refreshes polls
  and media otherwise, revises the ObjectRecord and re-resolves quotes. A
  community-wrapped Delete now tombstones the object, removes its ObjectRecord, reblogs
  and timeline rows, and lowers the reply count. Any deleted quoting post lowers the
  quoted post's quote count.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

PrivaPub/Federation/Actors/ActorDocument.cs

@@ -37,6 +37,7 @@ namespace PrivaPub.Federation.Actors
 		public List<CustomEmoji> Emojis { get; init; } = new();
 		public Dictionary<string, string> Fields { get; init; } = new();
 		public IReadOnlyList<ActorKey> Keys { get; init; } = Array.Empty<ActorKey>();
+		public List<string> Features { get; init; } = new();
 
 		public ActorKey Key(string keyId) => Keys.FirstOrDefault(k => k.Id == keyId);
 
@@ -54,6 +55,7 @@ namespace PrivaPub.Federation.Actors
 			{
 				Id = id,
 				Type = type,
+				Features = ActorFeatures.Detect(root),
 				PreferredUsername = RemoteActorService.Text(root, "preferredUsername"),
 				Name = RemoteActorService.Text(root, "name"),
 				Summary = RemoteActorService.Text(root, "summary"),

PrivaPub/Federation/Actors/ActorFeatures.cs

@@ -0,0 +1,72 @@
+using System.Security.Cryptography;
+using System.Text.Json;
+
+namespace PrivaPub.Federation.Actors
+{
+	public static class ActorFeatures
+	{
+		public static List<string> Detect(JsonElement root)
+		{
+			var found = new List<string>();
+			if (root.ValueKind != JsonValueKind.Object)
+				return found;
+			void When(bool condition, string feature)
+			{
+				if (condition)
+					found.Add(feature);
+			}
+			bool Has(string name) => root.TryGetProperty(name, out var value) && value.ValueKind is not (JsonValueKind.Null or JsonValueKind.Undefined);
+			bool True(string name) => root.TryGetProperty(name, out var value) && value.ValueKind == JsonValueKind.True;
+			IEnumerable<JsonElement> Items(string name) => !root.TryGetProperty(name, out var value)
+				? Enumerable.Empty<JsonElement>()
+				: value.ValueKind == JsonValueKind.Array ? value.EnumerateArray() : new[] { value };
+			bool Typed(JsonElement item, string type) =>
+				item.ValueKind == JsonValueKind.Object && item.TryGetProperty("type", out var t) && t.ValueKind == JsonValueKind.String && t.GetString() == type;
+
+			When(Has("featured"), "featured");
+			When(Has("featuredTags"), "featured-tags");
+			When(Items("alsoKnownAs").Any(), "also-known-as");
+			When(Has("movedTo"), "moved-to");
+			When(root.TryGetProperty("endpoints", out var endpoints) && endpoints.ValueKind == JsonValueKind.Object && endpoints.TryGetProperty("sharedInbox", out _), "shared-inbox");
+			When(Has("assertionMethod"), "fep-521a-assertion-method");
+			When(Has("proof"), "fep-8b32-proof");
+			When(Items("attachment").Any(a => Typed(a, "PropertyValue")), "property-value");
+			When(Items("attachment").Any(a => Typed(a, "VerifiableIdentityStatement") || Typed(a, "IdentityProof")), "fep-c390-identity-proof");
+			When(Items("tag").Any(t => Typed(t, "Emoji")), "custom-emoji");
+			When(root.EnumerateObject().Any(p => p.Name.StartsWith("_misskey", StringComparison.Ordinal)), "misskey");
+			When(True("isCat"), "is-cat");
+			When(Has("webfinger"), "fep-2c59-webfinger");
+			When(Has("attributionDomains"), "attribution-domains");
+			When(Has("searchableBy"), "fep-268d-searchable-by");
+			When(True("indexable"), "indexable");
+			When(root.TryGetProperty("discoverable", out var discoverable) && discoverable.ValueKind == JsonValueKind.False, "undiscoverable");
+			When(True("manuallyApprovesFollowers"), "locked");
+			When(True("memorial"), "memorial");
+			When(Has("generator"), "generator");
+			When(root.TryGetProperty("publicKey", out var keys) && keys.ValueKind == JsonValueKind.Array, "public-key-array");
+			if (KeyBits(root) is { } bits)
+				found.Add($"key:rsa-{bits}");
+			return found;
+		}
+
+		static int? KeyBits(JsonElement root)
+		{
+			if (!root.TryGetProperty("publicKey", out var key))
+				return default;
+			if (key.ValueKind == JsonValueKind.Array)
+				key = key.EnumerateArray().FirstOrDefault(k => k.ValueKind == JsonValueKind.Object);
+			if (key.ValueKind != JsonValueKind.Object || !key.TryGetProperty("publicKeyPem", out var pem) || pem.ValueKind != JsonValueKind.String)
+				return default;
+			try
+			{
+				using var rsa = RSA.Create();
+				rsa.ImportFromPem(pem.GetString());
+				return rsa.KeySize;
+			}
+			catch (Exception ex) when (ex is ArgumentException or CryptographicException)
+			{
+				return default;
+			}
+		}
+	}
+}

PrivaPub/Federation/Actors/RemoteActorService.cs

@@ -192,6 +192,7 @@ namespace PrivaPub.Federation.Actors
 				.Modify(a => a.Published, actor.Published)
 				.Modify(a => a.Emojis, actor.Emojis)
 				.Modify(a => a.Fields, actor.Fields)
+				.Modify(a => a.Features, actor.Features)
 				.Modify(a => a.AvatarType, Enum.TryParse<AvatarType>(actor.Type, out var type) ? type : AvatarType.Person)
 				.Modify(a => a.PublicKeyId, key?.Id)
 				.Modify(a => a.PublicKey, key?.Pem)