Everything on, phase 4b: ids that resolve, a hashtag page, grouped notifications, remote accounts' real counts

- A community's announces resolve, as FEDERATION.md and ROADMAP always said Announce ids do. GroupDistributor keeps
  each one it sends (GroupAnnouncement, unique by id). /grunts serves it while the post it carries is shown and 410
  after, and also serves the announce-{postId} ids the group outbox lists, which now keep a stable `published`
  instead of the time of the fetch.
- A persona's boost points at the boosted post: its `url` in the Mastodon API is the boosted post's page, and a browser
  following the boost's id is redirected there instead of getting JSON.
- /tags/{tag}, where every Hashtag link we send points, is now a public page of this server's public posts with that
  tag, with the same strict CSP and noindex as the profile pages.
- Grouped notifications (/api/v2/notifications, its unread count, a group, its accounts and dismiss). We advertise
  api_versions.mastodon = 7 so clients show quotes, and clients that trust it call these; they answered 404. Likes and
  boosts of one post group together, as do follows within an hour. The version string stays 4.2.0 until streaming
  and Web Push exist.
- A remote account's follower, following and post counts are what its server publishes. AccountCountsJob reads its
  collections' totalItems from its own origin, signed by the instance actor, at most daily and only after the account
  was fetched, never when someone looks. They used to be 0.
- The other ids that do not resolve are documented as such: Update, Delete, EmojiReact, QuoteRequest and its answers,
  Flag, Ignore and poll votes.

676 tests pass.

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

PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs

@@ -177,8 +177,7 @@ namespace PrivaPub.Api.Mastodon.Controllers
 			_dbEntities = dbEntities;
 		}
 
-		[HttpGet("/api/v1/notifications"), Scope("read:notifications")]
-		public async Task<IActionResult> List(CancellationToken token)
+		Find<NotificationEntity, NotificationEntity> Filtered()
 		{
 			var types = Params.List("types").Select(Parse).Where(t => t.HasValue).Select(t => t.Value).ToList();
 			var excluded = Params.List("exclude_types").Select(Parse).Where(t => t.HasValue).Select(t => t.Value).ToList();
@@ -189,11 +188,132 @@ namespace PrivaPub.Api.Mastodon.Controllers
 				query.Match(n => !excluded.Contains(n.Type));
 			if (Params.Get("account_id") is { } accountId)
 				query.Match(n => n.FromAccountId == accountId);
-			var notifications = await Page.From(Params, Limit(15, 30)).Fetch(query, n => n.ID, token);
+			return query;
+		}
+
+		[HttpGet("/api/v1/notifications"), Scope("read:notifications")]
+		public async Task<IActionResult> List(CancellationToken token)
+		{
+			var notifications = await Page.From(Params, Limit(15, 30)).Fetch(Filtered(), n => n.ID, token);
 			Link("/api/v1/notifications", notifications.LastOrDefault()?.ID, notifications.FirstOrDefault()?.ID);
 			return Json(await Map(notifications, token));
 		}
 
+		// Grouped notifications (Mastodon 4.3): api_versions.mastodon says we speak that API, so clients call it. Likes and
+		// boosts of one post group together, as do follows within an hour; everything else stands alone.
+		static readonly HashSet<string> DefaultGrouped = new() { "favourite", "reblog", "follow" };
+
+		HashSet<string> Grouped() => Params.List("grouped_types") is { Count: > 0 } chosen ? chosen.ToHashSet() : DefaultGrouped;
+
+		static string GroupKey(NotificationEntity n, ISet<string> grouped) =>
+			!grouped.Contains(Names[n.Type]) ? $"ungrouped-{n.ID}"
+			: n.Type == NotificationType.Follow ? $"grouped-follow-{n.CreatedAt:yyyyMMddHH}"
+			: string.IsNullOrEmpty(n.PostId) ? $"ungrouped-{n.ID}"
+			: $"grouped-{Names[n.Type]}-{n.PostId}";
+
+		// the notifications a group key stands for
+		System.Linq.Expressions.Expression<Func<NotificationEntity, bool>> InGroup(string key)
+		{
+			var me = MyId;
+			if (key.StartsWith("ungrouped-", StringComparison.Ordinal))
+			{
+				var id = key["ungrouped-".Length..];
+				return n => n.AvatarId == me && n.ID == id;
+			}
+			if (key.StartsWith("grouped-follow-", StringComparison.Ordinal)
+				&& DateTime.TryParseExact(key["grouped-follow-".Length..], "yyyyMMddHH", System.Globalization.CultureInfo.InvariantCulture,
+					System.Globalization.DateTimeStyles.AdjustToUniversal | System.Globalization.DateTimeStyles.AssumeUniversal, out var hour))
+			{
+				var end = hour.AddHours(1);
+				return n => n.AvatarId == me && n.Type == NotificationType.Follow && n.CreatedAt >= hour && n.CreatedAt < end;
+			}
+			if (key.Split('-') is ["grouped", var name, var postId] && Parse(name) is { } type)
+				return n => n.AvatarId == me && n.Type == type && n.PostId == postId;
+			return default;
+		}
+
+		async Task<List<NotificationEntity>> Members(string key, CancellationToken token) =>
+			InGroup(key) is { } filter
+				? await _dbEntities.Notifications.Match(filter).Sort(n => n.ID, Order.Descending).Limit(80).ExecuteAsync(token)
+				: new List<NotificationEntity>();
+
+		async Task<object> Groups(List<NotificationEntity> page, ISet<string> grouped, CancellationToken token)
+		{
+			var mapped = (await Map(page, token)).ToDictionary(n => n.Id);
+			var shown = page.Where(n => mapped.ContainsKey(n.ID)).ToList();
+			var groups = new List<object>();
+			foreach (var group in shown.GroupBy(n => GroupKey(n, grouped)))
+			{
+				var newest = mapped[group.First().ID];
+				var total = group.Key.StartsWith("ungrouped-", StringComparison.Ordinal) ? 1 : await DB.Default.CountAsync(InGroup(group.Key), token);
+				groups.Add(new
+				{
+					group_key = group.Key,
+					notifications_count = Math.Max(total, group.Count()),
+					type = newest.Type,
+					most_recent_notification_id = newest.Id,
+					page_min_id = group.Last().ID,
+					page_max_id = group.First().ID,
+					latest_page_notification_at = newest.CreatedAt,
+					sample_account_ids = group.Select(n => mapped[n.ID].Account.Id).Distinct().Take(8).ToList(),
+					status_id = newest.Status?.Id,
+					emoji = newest.Emoji,
+					emoji_url = newest.EmojiUrl
+				});
+			}
+			return new
+			{
+				accounts = mapped.Values.Select(n => n.Account).DistinctBy(a => a.Id).ToList(),
+				statuses = mapped.Values.Where(n => n.Status != default).Select(n => n.Status).DistinctBy(s => s.Id).ToList(),
+				notification_groups = groups
+			};
+		}
+
+		[HttpGet("/api/v2/notifications"), Scope("read:notifications")]
+		public async Task<IActionResult> GroupedList(CancellationToken token)
+		{
+			var notifications = await Page.From(Params, Limit(40, 80)).Fetch(Filtered(), n => n.ID, token);
+			Link("/api/v2/notifications", notifications.LastOrDefault()?.ID, notifications.FirstOrDefault()?.ID);
+			return Json(await Groups(notifications, Grouped(), token));
+		}
+
+		[HttpGet("/api/v2/notifications/unread_count"), Scope("read:notifications")]
+		public async Task<IActionResult> GroupedUnreadCount(CancellationToken token)
+		{
+			var unread = await Filtered().Match(n => !n.IsRead).Sort(n => n.ID, Order.Descending)
+				.Limit(Math.Clamp(Params.Int("limit") ?? 100, 1, 1000)).ExecuteAsync(token);
+			var shown = (await Map(unread, token)).Select(n => n.Id).ToHashSet();
+			var grouped = Grouped();
+			return Json(new { count = unread.Where(n => shown.Contains(n.ID)).Select(n => GroupKey(n, grouped)).Distinct().Count() });
+		}
+
+		[HttpGet("/api/v2/notifications/{groupKey}"), Scope("read:notifications")]
+		public async Task<IActionResult> Group(string groupKey, CancellationToken token)
+		{
+			var members = await Members(groupKey, token);
+			if (members.Count == 0)
+				return NotFoundError();
+			return Json(await Groups(members, new HashSet<string>(DefaultGrouped.Append(Names[members[0].Type])), token));
+		}
+
+		[HttpGet("/api/v2/notifications/{groupKey}/accounts"), Scope("read:notifications")]
+		public async Task<IActionResult> GroupAccounts(string groupKey, CancellationToken token)
+		{
+			var members = await Members(groupKey, token);
+			if (members.Count == 0)
+				return NotFoundError();
+			return Json((await Map(members, token)).Select(n => n.Account).DistinctBy(a => a.Id).ToList());
+		}
+
+		[HttpPost("/api/v2/notifications/{groupKey}/dismiss"), Scope("write:notifications")]
+		public async Task<IActionResult> DismissGroup(string groupKey, CancellationToken token)
+		{
+			if (InGroup(groupKey) is not { } filter)
+				return NotFoundError();
+			await DB.Default.DeleteAsync(filter);
+			return Json(new { });
+		}
+
 		[HttpGet("/api/v1/notifications/{id}"), Scope("read:notifications")]
 		public async Task<IActionResult> Get(string id, CancellationToken token)
 		{