Notifications in groups, and what is unread

The Notifications tab reads grouped notifications (/api/v2/notifications):
likes and boosts of one post, or follows of one hour, are one card naming
both accounts of a pair, or the newest and how many others, with their
avatars. A notification the stream tells joins its group and waits on top.
The tab's badge counts what is unread; opening the tab moves the
notifications marker to the newest shown, which reads it on PrivaPub.

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

Models/FeedPost.cs

@@ -17,7 +17,11 @@ public class FeedPost
 	/// <summary>The post shown; null for a notification without one (a follow).</summary>
 	public Status Status { get; set; }
 	public Account BoostedBy { get; init; }
-	public Notification Notification { get; init; }
+	public Notification Notification { get; set; }
+	/// <summary>For a notification standing for a group (likes of one post, follows of one hour): how many, and a few of
+	/// the accounts, newest first.</summary>
+	public int GroupCount { get; set; } = 1;
+	public List<Account> GroupAccounts { get; set; } = [];
 	public Conversation Conversation { get; init; }
 	/// <summary>A located post: within its range of the reader, never on the Mastodon API.</summary>
 	public bool Located { get; init; }
@@ -43,12 +47,38 @@ public class FeedPost
 
 	public static FeedPost Of(Notification notification) => new()
 	{
-		Key = notification.Id,
+		Key = notification.GroupKey ?? notification.Id,
 		CursorId = notification.Id,
 		Status = notification.Status?.Reblog ?? notification.Status,
-		Notification = notification
+		Notification = notification,
+		GroupAccounts = notification.Account is null ? [] : [notification.Account]
 	};
 
+	/// <summary>A group of notifications as one item: its newest notification, how many it holds, and a few accounts.</summary>
+	public static FeedPost Of(NotificationGroup group, IReadOnlyDictionary<string, Account> accounts, IReadOnlyDictionary<string, Status> statuses)
+	{
+		var sample = group.SampleAccountIds.Select(accounts.GetValueOrDefault).Where(a => a is not null).ToList();
+		var status = group.StatusId is null ? null : statuses.GetValueOrDefault(group.StatusId);
+		return new()
+		{
+			Key = group.GroupKey,
+			CursorId = group.MostRecentNotificationId,
+			Status = status?.Reblog ?? status,
+			Notification = new Notification
+			{
+				Id = group.MostRecentNotificationId,
+				Type = group.Type,
+				CreatedAt = group.LatestPageNotificationAt,
+				Account = sample.FirstOrDefault(),
+				Status = status,
+				Emoji = group.Emoji,
+				GroupKey = group.GroupKey
+			},
+			GroupCount = Math.Max(1, group.NotificationsCount),
+			GroupAccounts = sample
+		};
+	}
+
 	public static FeedPost Of(Conversation conversation) => new()
 	{
 		Key = conversation.Id,