Podcast episodes play; servers with NodeInfo2 only are described

Castopod announces an episode with a Note that only links to the episode's page, which serves a PodcastEpisode. PrivaPub
reads PodcastEpisode (its words in description, its sound in audio, its cover in image), and a Note that is only a link
to its author's own episode takes the episode's sound, title, cover and words, so the post plays. A server that
publishes no NodeInfo is described from NodeInfo2 (/.well-known/x-nodeinfo2), as Castopod publishes.

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

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -83,7 +83,7 @@ namespace PrivaPub.Federation.Inbox
 		{
 			var mentions = await Mentions(note, to.Concat(cc), _localActors, token);
 
-			return new PostEntity
+			var post = new PostEntity
 			{
 				ID = PrivacyIds.Arrived(note.Published),
 				ObjectURI = note.Id,
@@ -135,6 +135,31 @@ namespace PrivaPub.Federation.Inbox
 				UpdateDate = note.Updated ?? note.Published,
 				EditedAt = note.Updated
 			};
+			await Episode(post, note, author, token);
+			return post;
+		}
+
+		static readonly System.Text.RegularExpressions.Regex Href = new(@"href=""([^""]+)""", System.Text.RegularExpressions.RegexOptions.Compiled);
+
+		// a post that is only a link to a podcast episode of its own author (Castopod announces each episode so): the
+		// episode's sound, title and cover, read from it
+		async Task Episode(PostEntity post, NoteDocument note, ForeignAvatar author, CancellationToken token)
+		{
+			if (note.Type != "Note" || post.Media.Count > 0 || string.IsNullOrEmpty(note.ContentHtml))
+				return;
+			var links = Href.Matches(note.ContentHtml).Select(m => System.Net.WebUtility.HtmlDecode(m.Groups[1].Value)).Distinct().ToList();
+			if (links.Count != 1 || links[0] == note.Id || !Origin.Same(links[0], author.ActorURI))
+				return;
+			using var scope = HttpScope.For("object");
+			using var fetched = await _remoteActors.FetchObject(links[0], token);
+			var episode = fetched == default ? default : NoteParser.Parse(JsonNode.Parse(fetched.Root.GetRawText()));
+			if (episode is not { Type: "PodcastEpisode" } || episode.AttributedTo != author.ActorURI)
+				return;
+			post.Media = episode.Attachments.ToList();
+			post.Audio = episode.Audio;
+			post.Title ??= episode.Title;
+			post.CoverURL ??= episode.CoverURL;
+			post.Excerpt ??= ObjectShapes.Text(episode.ContentHtml, 1000);
 		}
 
 		public async Task<PostEntity> Parent(string inReplyTo, int depth, CancellationToken token)