P6: quote posts, received and sent (FEP-044f and the older keys)

- Received quotes: read from `quote`, `quoteUrl`, `quoteUri`, `_misskey_quote` or a FEP-e232 Link tag; the quoted post
  is fetched once; a quoteAuthorization stamp is verified field by field on the quoted author's origin; a consent
  quote without a stamp is pending; an older-key quote of a public post is shown; Delete of a stamp revokes. Counts
  and a `quote` notification follow the accepted state. The `quote-inline` fallback survives sanitising and is removed
  from content when the real quote is shown.
- Personas quote through `quoted_status_id`: posts that state a quote policy get a QuoteRequest and stay pending until
  an Accept brings a stamp we can verify, then an Update adds quoteAuthorization; posts that state none are quoted
  the older way, without `quote`; another persona's posts cannot be quoted yet (we issue no stamps). Quoting posts
  are delivered to the quoted author too.
- Mastodon API: Status.quote (with the quoted status one level deep), quotes_count, quote_approval from the remote
  policy, GET /api/v1/statuses/:id/quotes, `quote` notifications, and api_versions.mastodon = 7.

Checked live: GoToSocial's author-only quote policy is respected.

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

PrivaPub/Federation/Objects/ContentSanitizer.cs

@@ -38,7 +38,7 @@ namespace PrivaPub.Federation.Objects
 			{
 				KeepChildNodes = true
 			};
-			foreach (var allowed in new[] { "mention", "hashtag", "ellipsis", "invisible" })
+			foreach (var allowed in new[] { "mention", "hashtag", "ellipsis", "invisible", "quote-inline" })
 				sanitizer.AllowedClasses.Add(allowed);
 			sanitizer.RemovingCssClass += (_, e) => e.Cancel = MicroformatClass().IsMatch(e.CssClass);
 			sanitizer.RemovingTag += (_, e) =>

PrivaPub/Federation/Objects/NoteParser.cs

@@ -25,6 +25,9 @@ namespace PrivaPub.Federation.Objects
 		public string Context { get; init; }
 		public string Audience { get; init; }
 		public string QuoteUri { get; init; }
+		public string QuoteAuthorization { get; init; }
+		public bool QuotesByConsent { get; init; }//FEP-044f `quote`, as opposed to the legacy keys that ask nobody
+		public bool QuoteDeleted { get; init; }
 		public DateTime Published { get; init; }
 		public DateTime? Updated { get; init; }
 		public IReadOnlyList<string> To { get; init; } = Array.Empty<string>();
@@ -34,6 +37,7 @@ namespace PrivaPub.Federation.Objects
 		public IReadOnlyList<PostMedia> Attachments { get; init; } = Array.Empty<PostMedia>();
 		public PostSource Source { get; init; }
 		public PostPoll Poll { get; init; }
+		public InteractionRule QuotePolicy { get; init; }
 		public IReadOnlyList<CustomEmoji> Emojis { get; init; } = Array.Empty<CustomEmoji>();
 		public string CoverURL { get; init; }
 		public PostLink Link { get; init; }
@@ -79,7 +83,10 @@ namespace PrivaPub.Federation.Objects
 				InReplyTo = Id(note["inReplyTo"]),
 				Context = Id(note["context"]) ?? Value(note, "conversation"),
 				Audience = Id(note["audience"]),
-				QuoteUri = Value(note, "quote") ?? Value(note, "quoteUrl") ?? Value(note, "quoteUri") ?? Value(note, "_misskey_quote"),
+				QuoteUri = Id(note["quote"]) ?? Value(note, "quoteUrl") ?? Value(note, "quoteUri") ?? Value(note, "_misskey_quote") ?? QuoteLink(note),
+				QuoteAuthorization = Id(note["quoteAuthorization"]),
+				QuotesByConsent = note.ContainsKey("quote"),
+				QuoteDeleted = note["quote"] is JsonObject quoted && Value(quoted, "type") == "Tombstone",
 				Published = Time(Value(note, "published")) ?? DateTime.UtcNow,
 				Updated = Time(Value(note, "updated")),
 				To = List(note["to"]),
@@ -97,6 +104,7 @@ namespace PrivaPub.Federation.Objects
 				Attachments = Attachments(note),
 				Source = ObjectShapes.Source(note),
 				Poll = ObjectShapes.Poll(note),
+				QuotePolicy = ObjectShapes.QuotePolicy(note),
 				Emojis = ObjectShapes.Emojis(note["tag"]),
 				CoverURL = ObjectShapes.Cover(note),
 				Link = ObjectShapes.Link(note),
@@ -169,6 +177,12 @@ namespace PrivaPub.Federation.Objects
 			};
 		}
 
+		static string QuoteLink(JsonObject note) =>
+			Tags(note, "Link")
+				.Where(t => Value(t, "mediaType") is { } type && (type.StartsWith("application/activity+json") || type.StartsWith("application/ld+json")))
+				.Select(t => Value(t, "href"))
+				.FirstOrDefault(href => Origin.Of(href) != default);
+
 		static string FirstOf(JsonNode map) =>
 			map is JsonObject languages ? languages.Select(l => l.Value is JsonValue v && v.TryGetValue<string>(out var text) ? text : default).FirstOrDefault(t => t != default) : default;
 

PrivaPub/Federation/Objects/ObjectShapes.cs

@@ -18,6 +18,7 @@ namespace PrivaPub.Federation.Objects
 		const int CoverMaxWidth = 1280;
 		const int MaxEmojis = 64;
 		const int MaxPollOptions = 20;
+		const int MaxAudience = 32;
 
 		static readonly Dictionary<string, string> MediaTypesByExtension = new(StringComparer.OrdinalIgnoreCase)
 		{
@@ -97,6 +98,23 @@ namespace PrivaPub.Federation.Objects
 				.Take(MaxEmojis)
 				.ToList();
 
+		public static InteractionRule QuotePolicy(JsonObject note)
+		{
+			if (note["interactionPolicy"] is not JsonObject policy || policy["canQuote"] is not JsonObject canQuote)
+				return default;
+			static List<string> Who(JsonNode node) => node switch
+			{
+				JsonArray array => array.Select(Id).Where(id => id != default).Take(MaxAudience).ToList(),
+				JsonNode single when Id(single) is { } id => new List<string> { id },
+				_ => new List<string>()
+			};
+			return new InteractionRule
+			{
+				Automatic = Who(canQuote["automaticApproval"] ?? canQuote["always"]),
+				Manual = Who(canQuote["manualApproval"] ?? canQuote["approvalRequired"])
+			};
+		}
+
 		public static PostPoll Poll(JsonObject note)
 		{
 			if (Value(note, "type") != "Question")