Streaming: what happens, told as it happens

Mastodon's streaming API: /api/v1/streaming as a WebSocket (streams
subscribed in the URL or by message) and /api/v1/streaming/{stream} as
server-sent events, with health and the URL advertised. The user stream
tells posts reaching the persona's home (not those an exclusive list keeps
apart, which its list stream tells), notifications, edits and deletions;
public, hashtag and list streams tell what belongs in them. An in-process
hub carries ids only; each connection maps a post or a notification for its
own persona as it sends it, so nothing it may not see, or whose author it
blocked or muted, goes out. A deletion reaches only the streams that showed
the post. The token comes as access_token, header or WebSocket protocol.

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

PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs

@@ -40,6 +40,31 @@ namespace PrivaPub.Api.Mastodon.Mappers
 
 		public string ProxiedUrl(string url) => Proxied(url);
 
+		// notifications as the persona sees them: one whose account or post it can no longer see is left out
+		public async Task<List<Entities.Notification>> Notifications(List<Models.Social.Notification> notifications, string viewerId, CancellationToken token)
+		{
+			var accounts = await Accounts(notifications.Select(n => n.FromAccountId), token);
+			var postIds = notifications.Where(n => n.PostId != default).Select(n => n.PostId).Distinct().ToList();
+			var posts = postIds.Count == 0
+				? new List<PostEntity>()
+				: await _dbEntities.Posts.Match(p => postIds.Contains(p.ID)).Match(VisibilityPolicy.IsShown).ExecuteAsync(token);
+			var statuses = (await Statuses(posts, viewerId, token)).ToDictionary(s => s.Id);
+			return notifications
+				.Where(n => accounts.ContainsKey(n.FromAccountId ?? string.Empty) && (n.PostId == default || statuses.ContainsKey(n.PostId)))
+				.Select(n => new Entities.Notification
+				{
+					Id = n.ID,
+					Type = Controllers.NotificationsController.Names[n.Type],
+					CreatedAt = MastodonJson.Time(n.CreatedAt),
+					GroupKey = $"ungrouped-{n.ID}",
+					Account = accounts[n.FromAccountId],
+					Status = n.PostId == default ? default : statuses[n.PostId],
+					Emoji = n.Emoji == default ? default : n.EmojiURL == default ? n.Emoji : $":{n.Emoji}:",
+					EmojiUrl = Proxied(n.EmojiURL)
+				})
+				.ToList();
+		}
+
 		string MissingAvatar => $"{_localActors.BaseAddress}/media/missing-avatar.png";
 		string MissingHeader => $"{_localActors.BaseAddress}/media/missing-header.png";