R8 the Mastodon API made real: featured tags, endorsements, notes, notify and languages, suggestions, the direct stream

Featured tags per persona (/api/v1/featured_tags, suggestions, tags/:name/feature, accounts' featured tags, max 10),
listed at /tattoos as Hashtags and sent as Add/Remove{Hashtag} to followers on the featured collection, as Mastodon
sends them; remote accounts' tags received and read from featuredTags. Endorsements (pin/endorse) and private notes
(PersonaNote) kept per persona and never federated; the relationship's notifying, languages, endorsed and note, with
follow's notify (status notifications) and languages (home filter). Reading preferences set on /clientapi. Suggestions
v1/v2 with dismissals and staff picks, never the persona or a sibling. conversation events on the direct stream.
translate, annual reports and the admin API answer. New collections backed up and removed with their persona.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpVCoDeM1qUTRp4fXQdfof

PrivaPub/Domain/Social/FeaturedTags.cs

@@ -0,0 +1,264 @@
+using MongoDB.Driver;
+using MongoDB.Entities;
+
+using PrivaPub.Api.Mastodon.Controllers;
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Inbox;
+using PrivaPub.Federation.Objects;
+using PrivaPub.Federation.Outbox;
+using PrivaPub.Federation.Rendering;
+using PrivaPub.Infrastructure.Http;
+using PrivaPub.Models.Post;
+using PrivaPub.Models.Social;
+using PrivaPub.Models.User;
+using PrivaPub.StaticServices;
+
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+using static PrivaPub.Federation.Objects.ActivityJson;
+
+using PostEntity = PrivaPub.Models.Post.Post;
+
+namespace PrivaPub.Domain.Social
+{
+	public interface IFeaturedTags
+	{
+		/// <summary>The persona features a hashtag (already featured, it is as it was): the row, or why not.</summary>
+		Task<(FeaturedTag Tag, string Error)> Feature(LocalActor persona, string name, CancellationToken token);
+
+		/// <summary>The persona stops featuring a hashtag, named by the row's id or by its name: the row taken away, if any.</summary>
+		Task<FeaturedTag> Unfeature(LocalActor persona, string id, string name, CancellationToken token);
+
+		Task<List<FeaturedTag>> Of(string avatarId, CancellationToken token);
+
+		/// <summary>An account elsewhere features a hashtag (Add of a Hashtag) or stops (Remove).</summary>
+		Task Receive(JsonNode activity, ForeignAvatar owner, bool add, CancellationToken token);
+
+		/// <summary>An account elsewhere's featuredTags collection, read again (with its counts, at most daily).</summary>
+		Task Sync(ForeignAvatar owner, CancellationToken token);
+	}
+
+	// Featured hashtags (Mastodon's featured tags, completion program R8). A persona's are public: its featuredTags
+	// collection (/peasants/{name}/tattoos) lists them as Hashtag objects, and featuring one sends Add{Hashtag} to its
+	// followers, unfeaturing it Remove{Hashtag}, both with its `featured` collection (/trophies) as the target: that is how
+	// Mastodon sends them (its AddHashtagSerializer), and the only target Mastodon takes a Hashtag from. Received the same
+	// way, with either collection as the target, and read from an account's featuredTags collection with its counts.
+	public class FeaturedTags : IFeaturedTags
+	{
+		public const int MaxFeatured = 10;//the instance API's max_featured_tags, Mastodon's FeaturedTag::LIMIT
+		public const int MaxRemote = 20;//what we keep of an account elsewhere, whatever its server allows
+
+		readonly IDeliveryService _delivery;
+		readonly IRemoteActorService _remoteActors;
+
+		public FeaturedTags(IDeliveryService delivery, IRemoteActorService remoteActors)
+		{
+			_delivery = delivery;
+			_remoteActors = remoteActors;
+		}
+
+		// a featured hashtag as Mastodon renders it (its HashtagSerializer): the link to this server's page of the tag, which
+		// is what our posts' Hashtag tags link to, and the name as the persona wrote it
+		public static JsonObject Hashtag(string baseAddress, FeaturedTag tag) => new()
+		{
+			["type"] = "Hashtag",
+			["href"] = ActivityPubRenderer.TagUrl(baseAddress, tag.Name),
+			["name"] = "#" + (string.IsNullOrEmpty(tag.DisplayName) ? tag.Name : tag.DisplayName)
+		};
+
+		public async Task<List<FeaturedTag>> Of(string avatarId, CancellationToken token) =>
+			await DB.Default.Find<FeaturedTag>().Match(t => t.AvatarId == avatarId).Sort(t => t.ID, Order.Ascending).ExecuteAsync(token);
+
+		public async Task<(FeaturedTag Tag, string Error)> Feature(LocalActor persona, string name, CancellationToken token)
+		{
+			var display = name?.Trim().TrimStart('#');
+			var normal = TagsController.Normalise(display);
+			if (!TagsController.IsHashtag(normal))
+				return (default, "Validation failed: Tag is invalid");
+			var existing = await DB.Default.Find<FeaturedTag>().Match(t => t.AvatarId == persona.Id && t.Name == normal).ExecuteFirstAsync(token);
+			if (existing != default)
+				return (existing, default);
+			if (await DB.Default.CountAsync<FeaturedTag>(t => t.AvatarId == persona.Id, token) >= MaxFeatured)
+				return (default, $"Validation failed: You can feature at most {MaxFeatured} hashtags");
+			var tag = new FeaturedTag
+			{
+				AvatarId = persona.Id,
+				Name = normal,
+				DisplayName = display.Length <= 100 ? display : normal
+			};
+			try
+			{
+				await DB.Default.SaveAsync(tag, token);
+			}
+			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
+			{
+				return (await DB.Default.Find<FeaturedTag>().Match(t => t.AvatarId == persona.Id && t.Name == normal).ExecuteFirstAsync(token), default);
+			}
+			await Tell(persona, tag, add: true, token);
+			return (tag, default);
+		}
+
+		public async Task<FeaturedTag> Unfeature(LocalActor persona, string id, string name, CancellationToken token)
+		{
+			var normal = id == default ? TagsController.Normalise(name) : default;
+			var tag = id != default
+				? await DB.Default.Find<FeaturedTag>().Match(t => t.ID == id && t.AvatarId == persona.Id).ExecuteFirstAsync(token)
+				: await DB.Default.Find<FeaturedTag>().Match(t => t.AvatarId == persona.Id && t.Name == normal).ExecuteFirstAsync(token);
+			if (tag == default)
+				return default;
+			var removed = await DB.Default.DeleteAsync<FeaturedTag>(t => t.ID == tag.ID);
+			if (removed.DeletedCount > 0)
+				await Tell(persona, tag, add: false, token);
+			return tag;
+		}
+
+		// to the persona's followers, as Mastodon distributes it (AccountRawDistributionWorker); a suspended persona's goes
+		// nowhere (DeliveryService.HeldBack)
+		async Task Tell(LocalActor persona, FeaturedTag tag, bool add, CancellationToken token)
+		{
+			if (persona is not { IsFederated: true, Kind: Models.Federation.LocalActorKind.Person })
+				return;
+			await _delivery.EnqueueToFollowers(persona, new JsonObject
+			{
+				["@context"] = ActivityPubRenderer.Context(),
+				["id"] = persona.ActivityUri($"{(add ? "feature" : "unfeature")}-tag-{tag.ID}-{DateTime.UtcNow.Ticks}"),
+				["type"] = add ? "Add" : "Remove",
+				["actor"] = persona.Uri,
+				["object"] = Hashtag(persona.BaseAddress, tag),
+				["target"] = persona.Featured,
+				["to"] = new JsonArray(ActivityPubRenderer.Public),
+				["cc"] = new JsonArray(persona.Followers)
+			}, token);
+		}
+
+		// what posts carry the tag: a persona's own public and unlisted posts, or the public and unlisted posts we hold of an
+		// account elsewhere, as Mastodon counts a featured tag (statuses_count, last_status_at)
+		public static async Task<Dictionary<string, (long Count, DateTime? Last)>> Usage(string avatarId, string actorUri, IReadOnlyCollection<string> names,
+			DbEntities dbEntities, CancellationToken token)
+		{
+			var usage = new Dictionary<string, (long, DateTime?)>(StringComparer.Ordinal);
+			foreach (var name in names.Distinct(StringComparer.Ordinal))
+			{
+				var tag = name;
+				var query = avatarId != default
+					? dbEntities.Posts.Match(p => p.GroupUserId == avatarId && !p.IsFederatedCopy)
+					: dbEntities.Posts.Match(p => p.ActorURI == actorUri && p.IsFederatedCopy);
+				query.Match(p => p.Tags.Contains(tag) && p.ReblogOfPostId == null
+					&& (p.Visibility == PostVisibility.Public || p.Visibility == PostVisibility.Unlisted)).Match(Privacy.VisibilityPolicy.IsShown);
+				var latest = await query.Sort(p => p.ID, Order.Descending).Limit(1).ExecuteFirstAsync(token);
+				if (latest == default)
+				{
+					usage[name] = (0, default);
+					continue;
+				}
+				var counted = avatarId != default
+					? await DB.Default.CountAsync<PostEntity>(f => f.Where(p => p.GroupUserId == avatarId && !p.IsFederatedCopy && p.Tags.Contains(tag)
+						&& p.ReblogOfPostId == null && (p.Visibility == PostVisibility.Public || p.Visibility == PostVisibility.Unlisted))
+						& f.Where(Privacy.VisibilityPolicy.IsShown), token)
+					: await DB.Default.CountAsync<PostEntity>(f => f.Where(p => p.ActorURI == actorUri && p.IsFederatedCopy && p.Tags.Contains(tag)
+						&& p.ReblogOfPostId == null && (p.Visibility == PostVisibility.Public || p.Visibility == PostVisibility.Unlisted))
+						& f.Where(Privacy.VisibilityPolicy.IsShown), token);
+				usage[name] = (counted, latest.CreationDate);
+			}
+			return usage;
+		}
+
+		public async Task Receive(JsonNode activity, ForeignAvatar owner, bool add, CancellationToken token)
+		{
+			var (normal, display) = Named(Value(activity["object"], "name"));
+			if (normal == default)
+			{
+				Arrival.Drop("unparseable");
+				return;
+			}
+			if (!add)
+			{
+				var removed = await DB.Default.DeleteAsync<RemoteFeaturedTag>(t => t.ActorURI == owner.ActorURI && t.Name == normal);
+				if (removed is { IsAcknowledged: true, DeletedCount: > 0 })
+					Arrival.Accept("tag-unfeatured");
+				else
+					Arrival.Drop("unknown-tag");
+				return;
+			}
+			if (await DB.Default.CountAsync<RemoteFeaturedTag>(t => t.ActorURI == owner.ActorURI, token) >= MaxRemote)
+			{
+				Arrival.Drop("too-many-tags");
+				return;
+			}
+			var first = await DB.Default.Find<RemoteFeaturedTag>().Match(t => t.ActorURI == owner.ActorURI).Sort(t => t.Position, Order.Ascending).ExecuteFirstAsync(token);
+			try
+			{
+				await DB.Default.SaveAsync(new RemoteFeaturedTag
+				{
+					ActorURI = owner.ActorURI,
+					Name = normal,
+					DisplayName = display,
+					Href = Link(Value(activity["object"], "href")),
+					Position = (first?.Position ?? 0) - 1
+				}, token);
+				Arrival.Accept("tag-featured");
+			}
+			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
+			{
+				Arrival.Drop("duplicate");
+			}
+		}
+
+		public async Task Sync(ForeignAvatar owner, CancellationToken token)
+		{
+			if (string.IsNullOrEmpty(owner.FeaturedTagsURL) || !Origin.Same(owner.FeaturedTagsURL, owner.ActorURI))
+				return;
+			var items = await Items(owner, token);
+			if (items == default)
+				return;
+			var tags = new List<RemoteFeaturedTag>();
+			foreach (var item in items)
+			{
+				if (Value(item, "type") != "Hashtag" || Named(Value(item, "name")) is not ({ } normal, var display) || tags.Any(t => t.Name == normal))
+					continue;
+				tags.Add(new RemoteFeaturedTag { ActorURI = owner.ActorURI, Name = normal, DisplayName = display, Href = Link(Value(item, "href")), Position = tags.Count });
+				if (tags.Count >= MaxRemote)
+					break;
+			}
+			await DB.Default.DeleteAsync<RemoteFeaturedTag>(t => t.ActorURI == owner.ActorURI);
+			if (tags.Count > 0)
+				await DB.Default.SaveAsync(tags, token);
+		}
+
+		static (string Normal, string Display) Named(string name)
+		{
+			var display = name?.Trim().TrimStart('#');
+			var normal = TagsController.Normalise(display);
+			return TagsController.IsHashtag(normal) ? (normal, display.Length <= 100 ? display : normal) : (default, default);
+		}
+
+		static string Link(string href) => Uri.TryCreate(href, UriKind.Absolute, out var uri) && uri.Scheme is "https" or "http" ? href : default;
+
+		// the collection's items, from it or its first page (its own server only), and the pages after, as Mastodon reads them
+		async Task<List<JsonNode>> Items(ForeignAvatar owner, CancellationToken token)
+		{
+			using var scope = HttpScope.For("collection");
+			var collection = await Fetch(owner.FeaturedTagsURL, token);
+			if (collection == default)
+				return default;
+			var items = new List<JsonNode>();
+			var page = collection["first"] is JsonObject embedded ? embedded
+				: Id(collection["first"]) is { } first && Origin.Same(first, owner.ActorURI) ? await Fetch(first, token)
+				: collection;
+			for (var pages = 0; page != default && pages < 3 && items.Count < MaxRemote; pages++)
+			{
+				if ((page["orderedItems"] ?? page["items"]) is JsonArray list)
+					items.AddRange(list.Where(i => i is JsonObject));
+				page = Id(page["next"]) is { } next && Origin.Same(next, owner.ActorURI) ? await Fetch(next, token) : default;
+			}
+			return items;
+		}
+
+		async Task<JsonObject> Fetch(string uri, CancellationToken token)
+		{
+			using var fetched = await _remoteActors.FetchObject(uri, token);
+			return fetched == default || fetched.Root.ValueKind != JsonValueKind.Object ? default : JsonNode.Parse(fetched.Root.GetRawText()) as JsonObject;
+		}
+	}
+}

PrivaPub/Domain/Social/FollowService.cs

@@ -26,7 +26,10 @@ namespace PrivaPub.Domain.Social
 		Task<WebResult> Follow(string rootUserId, FollowForm form, CancellationToken token);
 		Task<WebResult> Unfollow(string rootUserId, FollowForm form, CancellationToken token);
 		Task<WebResult> Followings(string rootUserId, string avatarId, CancellationToken token);
-		Task<Following> FollowAs(LocalActor follower, string target, bool showReblogs, CancellationToken token);
+		/// <summary>Follows an account, or changes how a follow already made shows it: notify and languages (R8) change only
+		/// when given (languages empty: every language).</summary>
+		Task<Following> FollowAs(LocalActor follower, string target, bool showReblogs, CancellationToken token, bool? notify = default,
+			IReadOnlyList<string> languages = default);
 		Task UnfollowAs(LocalActor follower, string target, CancellationToken token);
 		Task<bool> Decide(LocalActor me, string followerAccountId, bool accept, CancellationToken token);
 		Task<int> ResendPending(DateTime now, CancellationToken token);
@@ -93,7 +96,18 @@ namespace PrivaPub.Domain.Social
 			}
 		}
 
-		public async Task<Following> FollowAs(LocalActor follower, string target, bool showReblogs, CancellationToken token)
+		// a follow's languages as kept: their primary subtags, lower case; none, every language (null)
+		public static List<string> Languages(IReadOnlyList<string> languages)
+		{
+			var kept = (languages ?? Array.Empty<string>())
+				.Select(l => l?.Trim().Replace('_', '-').Split('-')[0].ToLowerInvariant())
+				.Where(l => l is { Length: >= 2 and <= 3 } && l.All(char.IsAsciiLetterLower))
+				.Distinct().Take(20).ToList();
+			return kept.Count == 0 ? null : kept;
+		}
+
+		public async Task<Following> FollowAs(LocalActor follower, string target, bool showReblogs, CancellationToken token, bool? notify = default,
+			IReadOnlyList<string> languages = default)
 		{
 			var (local, remote) = await ResolveTarget(target, token);
 			if (local == default && remote == default)
@@ -108,6 +122,17 @@ namespace PrivaPub.Domain.Social
 				if (existing.ShowReblogs != showReblogs)
 					await DB.Default.Update<Following>().MatchID(existing.ID).Modify(f => f.ShowReblogs, showReblogs).ExecuteAsync(token);
 				existing.ShowReblogs = showReblogs;
+				if (notify is { } notifying && existing.Notify != notifying)
+				{
+					await DB.Default.Update<Following>().MatchID(existing.ID).Modify(f => f.Notify, notifying).ExecuteAsync(token);
+					existing.Notify = notifying;
+				}
+				if (languages != default)
+				{
+					var kept = Languages(languages);
+					await DB.Default.Update<Following>().MatchID(existing.ID).Modify(f => f.Languages, kept).ExecuteAsync(token);
+					existing.Languages = kept;
+				}
 				// a request still unanswered is sent again, at most once an hour: a server can take a Follow (202) and
 				// drop it later, as one that cannot yet read our actor does; one that holds it already ignores the copy
 				if (existing.State == FollowState.Requested && remote != default)
@@ -125,6 +150,8 @@ namespace PrivaPub.Domain.Social
 				TargetIsLocal = local != default,
 				TargetInboxURL = local?.Inbox ?? remote.InboxURL,
 				ShowReblogs = showReblogs,
+				Notify = notify == true,
+				Languages = Languages(languages),
 				State = local is { ManuallyApprovesFollowers: false } ? FollowState.Accepted : FollowState.Requested
 			};
 			following.ID = (string)following.GenerateNewID();
@@ -157,6 +184,8 @@ namespace PrivaPub.Domain.Social
 
 			await DB.Default.DeleteAsync<Following>(following.ID);
 			await DB.Default.DeleteAsync<PersonaListMember>(m => m.AvatarId == follower.Id && m.AccountId == following.TargetAccountId);
+			// an endorsement holds only while the follow does, as on Mastodon (R8)
+			await DB.Default.DeleteAsync<Endorsement>(e => e.AvatarId == follower.Id && e.TargetActorURI == targetUri);
 			if (following.TargetIsLocal)
 			{
 				await DB.Default.DeleteAsync<Follower>(f => f.LocalActorId == following.TargetAccountId && f.ActorURI == follower.Uri);

PrivaPub/Domain/Social/Suggestions.cs

@@ -0,0 +1,149 @@
+using MongoDB.Driver;
+using MongoDB.Entities;
+
+using PrivaPub.Domain.Privacy;
+using PrivaPub.Federation.Actors;
+using PrivaPub.Models.Post;
+using PrivaPub.Models.Social;
+using PrivaPub.Models.User;
+
+using PostEntity = PrivaPub.Models.Post.Post;
+
+namespace PrivaPub.Domain.Social
+{
+	// Follow suggestions (completion program R8, Mastodon's /api/v1 and /api/v2/suggestions), best first:
+	// - staff: the accounts the administrators pick (ServerSettings.StaffPicks), Mastodon's `featured`;
+	// - past interactions: accounts the persona favourited, boosted or answered and does not follow;
+	// - global: accounts followed by at least GlobalMinimumFollowers personas here (`most_followed`), and personas here whose
+	//   public posts of the last 30 days were favourited and boosted the most (`most_interactions`); discoverable ones only.
+	// Never the persona itself, never a sibling persona of its login (suggesting one would pair them the moment the persona
+	// followed it; the server knows the pair, the persona's suggestions must not use it), never an account it follows, asked
+	// to follow, blocked, muted, was blocked by or dismissed, and never an account held back (suspended, a banned login's) or
+	// silenced (the API mapper shows it `limited`). Nothing here is shown to anyone but the persona asking.
+	public static class Suggestions
+	{
+		public const string Staff = "staff";
+		public const string PastInteractions = "past_interactions";
+		public const string Global = "global";
+		public const int GlobalMinimumFollowers = 3;
+
+		const int Recent = 200;
+		const int GlobalSize = 100;
+		static readonly TimeSpan GlobalLifetime = TimeSpan.FromMinutes(10);
+		static (DateTime At, List<(string Id, string Why)> Ids) _global = (DateTime.MinValue, new());
+
+		public sealed record Candidate(string AccountId, string Source, List<string> Sources);
+
+		// every candidate for the persona, in order, each once (with every reason it has), none of those it must never see
+		public static async Task<List<Candidate>> For(LocalActor me, IReadOnlyList<string> staffPicks, CancellationToken token)
+		{
+			var excluded = await Excluded(me, token);
+			var found = new List<Candidate>();
+			var byId = new Dictionary<string, Candidate>(StringComparer.Ordinal);
+			void Add(string id, string source, string why)
+			{
+				if (string.IsNullOrEmpty(id) || excluded.Contains(id))
+					return;
+				if (byId.TryGetValue(id, out var known))
+				{
+					if (!known.Sources.Contains(why))
+						known.Sources.Add(why);
+					return;
+				}
+				var candidate = new Candidate(id, source, new List<string> { why });
+				byId[id] = candidate;
+				found.Add(candidate);
+			}
+			foreach (var id in staffPicks ?? Array.Empty<string>())
+				Add(id, Staff, "featured");
+			foreach (var id in await Interacted(me.Id, token))
+				Add(id, PastInteractions, PastInteractions);//(Mastodon's sources has no word for it since 4.3; its source does)
+			foreach (var (id, why) in await GlobalCandidates(token))
+				Add(id, Global, why);
+			return found;
+		}
+
+		static async Task<HashSet<string>> Excluded(LocalActor me, CancellationToken token)
+		{
+			var excluded = new HashSet<string>(StringComparer.Ordinal) { me.Id };
+			var roots = (await DB.Default.Find<RootToAvatar>().Match(r => r.AvatarId == me.Id).ExecuteAsync(token)).Select(r => r.RootId).ToList();
+			if (roots.Count > 0)
+				excluded.UnionWith((await DB.Default.Find<RootToAvatar>().Match(r => roots.Contains(r.RootId)).ExecuteAsync(token)).Select(r => r.AvatarId));
+			excluded.UnionWith((await DB.Default.Find<Following>().Match(f => f.AvatarId == me.Id).Project(f => f.Include(x => x.TargetAccountId))
+				.ExecuteAsync(token)).Select(f => f.TargetAccountId));
+			excluded.UnionWith((await DB.Default.Find<Block>().Match(b => b.AvatarId == me.Id).ExecuteAsync(token)).Select(b => b.TargetAccountId));
+			// (a persona here that blocked this one)
+			excluded.UnionWith((await DB.Default.Find<Block>().Match(b => b.TargetActorURI == me.Uri).ExecuteAsync(token)).Select(b => b.AvatarId));
+			excluded.UnionWith((await DB.Default.Find<BlockedBy>().Match(b => b.AvatarId == me.Id).ExecuteAsync(token)).Select(b => b.AccountId));
+			excluded.UnionWith((await DB.Default.Find<Mute>().Match(m => m.AvatarId == me.Id).ExecuteAsync(token)).Select(m => m.TargetAccountId));
+			excluded.UnionWith((await DB.Default.Find<SuggestionDismissal>().Match(d => d.AvatarId == me.Id).ExecuteAsync(token)).Select(d => d.AccountId));
+			excluded.UnionWith(await Counted.HeldBackPersonas(token));
+			excluded.Remove(default);
+			return excluded;
+		}
+
+		// the accounts whose posts the persona favourited, boosted or answered lately, the most often first
+		static async Task<List<string>> Interacted(string avatarId, CancellationToken token)
+		{
+			var authors = new List<(string Id, int Age)>();
+			var liked = (await DB.Default.Find<Favourite>().Match(f => f.AccountId == avatarId).Sort(f => f.ID, Order.Descending).Limit(Recent)
+				.ExecuteAsync(token)).Select(f => f.PostId).ToList();
+			var boosted = (await DB.Default.Find<PostEntity>().Match(p => p.AuthorAccountId == avatarId && p.ReblogOfPostId != null && !p.DeletedAt.HasValue)
+				.Sort(p => p.ID, Order.Descending).Limit(Recent).Project(p => p.Include(x => x.ReblogOfPostId)).ExecuteAsync(token)).Select(p => p.ReblogOfPostId).ToList();
+			var interacted = liked.Concat(boosted).Distinct().ToList();
+			var posts = interacted.Count == 0 ? new Dictionary<string, PostEntity>()
+				: (await DB.Default.Find<PostEntity>().Match(p => interacted.Contains(p.ID))
+					.Project(p => p.Include(x => x.AuthorAccountId).Include(x => x.GroupUserId).Include(x => x.ReblogOfPostId)).ExecuteAsync(token))
+					.ToDictionary(p => p.ID);
+			authors.AddRange(interacted.Select((id, age) => (posts.GetValueOrDefault(id) is { ReblogOfPostId: null } post ? post.AuthorAccountId ?? post.GroupUserId : default, age)));
+			var answered = await DB.Default.Find<PostEntity>().Match(p => p.GroupUserId == avatarId && !p.IsFederatedCopy && p.InReplyToAccountId != null && !p.DeletedAt.HasValue)
+				.Sort(p => p.ID, Order.Descending).Limit(Recent).Project(p => p.Include(x => x.InReplyToAccountId)).ExecuteAsync(token);
+			authors.AddRange(answered.Select((p, age) => (p.InReplyToAccountId, age)));
+			return authors.Where(a => !string.IsNullOrEmpty(a.Id) && a.Id != avatarId)
+				.GroupBy(a => a.Id).OrderByDescending(g => g.Count()).ThenBy(g => g.Min(a => a.Age)).Select(g => g.Key).ToList();
+		}
+
+		// the same for every persona, worked out at most every ten minutes
+		static async Task<List<(string Id, string Why)>> GlobalCandidates(CancellationToken token)
+		{
+			var cached = _global;
+			if (DateTime.UtcNow - cached.At < GlobalLifetime)
+				return cached.Ids;
+			var ids = new List<(string, string)>();
+
+			var followed = await DB.Default.Fluent<Following>()
+				.Match(f => f.State == FollowState.Accepted && f.FollowerKind == null)
+				.Group(f => f.TargetAccountId, g => new { Id = g.Key, Count = g.Count() })
+				.Match(g => g.Count >= GlobalMinimumFollowers)
+				.SortByDescending(g => g.Count)
+				.Limit(GlobalSize)
+				.ToListAsync(token);
+			var followedIds = followed.Select(f => f.Id).ToList();
+			var discoverable = (await DB.Default.Find<Avatar>().Match(a => followedIds.Contains(a.ID) && a.Settings.IsDiscoverable && !a.DeletionAt.HasValue
+					&& !a.SilencedAt.HasValue && !a.SuspendedAt.HasValue).Project(a => a.Include(x => x.ID)).ExecuteAsync(token)).Select(a => a.ID)
+				.Concat((await DB.Default.Find<ForeignAvatar>().Match(f => followedIds.Contains(f.ID) && f.IsDiscoverable && !f.DeletionAt.HasValue
+					&& !f.SilencedAt.HasValue && !f.SuspendedAt.HasValue
+					&& (f.AvatarType == AvatarType.Person || f.AvatarType == AvatarType.Service || f.AvatarType == AvatarType.Organization))
+					.Project(f => f.Include(x => x.ID)).ExecuteAsync(token)).Select(f => f.ID))
+				.ToHashSet(StringComparer.Ordinal);
+			ids.AddRange(followed.Where(f => discoverable.Contains(f.Id)).Select(f => (f.Id, "most_followed")));
+
+			var since = DateTime.UtcNow.AddDays(-30);
+			var interactions = await DB.Default.Fluent<PostEntity>()
+				.Match(p => !p.IsFederatedCopy && p.GroupUserId != null && p.Visibility == PostVisibility.Public && p.ReblogOfPostId == null
+					&& !p.DeletedAt.HasValue && !p.AuthorLimited && !p.AuthorSuspended && p.CreationDate >= since)
+				.Group(p => p.GroupUserId, g => new { Id = g.Key, Count = g.Sum(p => p.FavouritesCount + p.ReblogsCount) })
+				.Match(g => g.Count > 0)
+				.SortByDescending(g => g.Count)
+				.Limit(GlobalSize)
+				.ToListAsync(token);
+			var active = interactions.Select(i => i.Id).ToList();
+			var shown = (await DB.Default.Find<Avatar>().Match(a => active.Contains(a.ID) && a.Settings.IsDiscoverable && !a.DeletionAt.HasValue
+				&& !a.SilencedAt.HasValue && !a.SuspendedAt.HasValue).Project(a => a.Include(x => x.ID)).ExecuteAsync(token)).Select(a => a.ID).ToHashSet();
+			ids.AddRange(interactions.Where(i => shown.Contains(i.Id)).Select(i => (i.Id, "most_interactions")));
+
+			_global = (DateTime.UtcNow, ids);
+			return ids;
+		}
+	}
+}