Lists: a persona's followed accounts, read apart

Mastodon's lists replace the empty stubs: CRUD, members (only accounts the
persona follows; a follow that ends takes its memberships with it),
accounts/:id/lists, and timelines/list/:id from the persona's home entries
with the replies policy (followed, list, none; self-replies and replies to
the persona always). An exclusive list's members stay out of home. Lists
never federate, and go with a deleted persona.

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

PrivaPub/Api/Mastodon/Controllers/AccountsController.cs

@@ -342,9 +342,6 @@ namespace PrivaPub.Api.Mastodon.Controllers
 		[HttpGet("/api/v1/accounts/{id}/featured_tags"), Scope("read:accounts", requiresUser: false), Microsoft.AspNetCore.Authorization.AllowAnonymous]
 		public IActionResult FeaturedTags(string id) => Json(Array.Empty<object>());
 
-		[HttpGet("/api/v1/accounts/{id}/lists"), Scope("read:lists")]
-		public IActionResult Lists(string id) => Json(Array.Empty<object>());
-
 		[HttpGet("/api/v1/accounts/familiar_followers"), Scope("read:follows")]
 		public IActionResult FamiliarFollowers() => Json(Params.List("id").Select(id => new { id, accounts = Array.Empty<Account>() }).ToList());
 

PrivaPub/Api/Mastodon/Controllers/ListsController.cs

@@ -0,0 +1,189 @@
+using Microsoft.AspNetCore.Mvc;
+
+using MongoDB.Entities;
+
+using PrivaPub.Api.Mastodon.Infrastructure;
+using PrivaPub.Api.Mastodon.Mappers;
+using PrivaPub.Domain.Privacy;
+using PrivaPub.Models.Social;
+using PrivaPub.StaticServices;
+
+namespace PrivaPub.Api.Mastodon.Controllers
+{
+	// Mastodon's lists (owner decision 2026-10-04, back from the cut list): a persona groups accounts it follows, reads them
+	// as a timeline, and may keep an exclusive list's members out of its home. Nothing here leaves the server.
+	public class ListsController : MastodonController
+	{
+		const int MaxLists = 50;
+		const int MaxMembers = 500;
+
+		readonly DbEntities _dbEntities;
+		readonly MastodonMapper _mapper;
+
+		public ListsController(DbEntities dbEntities, MastodonMapper mapper)
+		{
+			_dbEntities = dbEntities;
+			_mapper = mapper;
+		}
+
+		static object View(PersonaList list) => new { id = list.ID, title = list.Title, replies_policy = list.RepliesPolicy, exclusive = list.Exclusive };
+
+		Task<PersonaList> Mine(string id, CancellationToken token) =>
+			DB.Default.Find<PersonaList>().Match(l => l.ID == id && l.AvatarId == MyId).ExecuteFirstAsync(token);
+
+		// a list holds only accounts the persona still follows: whatever ended the follow (an unfollow, a Reject, a Block, the
+		// account's deletion), its membership goes with it, pruned here on the next read
+		async Task<List<string>> Members(PersonaList list, CancellationToken token)
+		{
+			var members = (await DB.Default.Find<PersonaListMember>().Match(m => m.ListId == list.ID).ExecuteAsync(token)).Select(m => m.AccountId).ToList();
+			if (members.Count == 0)
+				return members;
+			var followed = (await _dbEntities.Followings.Match(f => f.AvatarId == MyId && f.State == FollowState.Accepted && members.Contains(f.TargetAccountId))
+				.ExecuteAsync(token)).Select(f => f.TargetAccountId).ToHashSet();
+			var gone = members.Where(m => !followed.Contains(m)).ToList();
+			if (gone.Count > 0)
+				await DB.Default.DeleteAsync<PersonaListMember>(m => m.ListId == list.ID && gone.Contains(m.AccountId));
+			return members.Where(followed.Contains).ToList();
+		}
+
+		[HttpGet("/api/v1/lists"), Scope("read:lists")]
+		public async Task<IActionResult> All(CancellationToken token) =>
+			Json((await DB.Default.Find<PersonaList>().Match(l => l.AvatarId == MyId).Sort(l => l.Title, MongoDB.Entities.Order.Ascending)
+				.ExecuteAsync(token)).Select(View).ToList());
+
+		[HttpGet("/api/v1/lists/{id}"), Scope("read:lists")]
+		public async Task<IActionResult> One(string id, CancellationToken token) =>
+			await Mine(id, token) is { } list ? Json(View(list)) : NotFoundError();
+
+		[HttpPost("/api/v1/lists"), Scope("write:lists")]
+		public async Task<IActionResult> Create(CancellationToken token)
+		{
+			var title = Params.Get("title")?.Trim();
+			var policy = Params.Get("replies_policy") ?? ListRepliesPolicy.List;
+			if (string.IsNullOrEmpty(title) || title.Length > 200)
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Title can't be blank");
+			if (!ListRepliesPolicy.IsValid(policy))
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Replies policy is not included in the list");
+			if (await DB.Default.CountAsync<PersonaList>(l => l.AvatarId == MyId, token) >= MaxLists)
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Too many lists");
+			var list = new PersonaList { AvatarId = MyId, Title = title, RepliesPolicy = policy, Exclusive = Params.Bool("exclusive") == true };
+			await DB.Default.SaveAsync(list, token);
+			return Json(View(list));
+		}
+
+		[HttpPut("/api/v1/lists/{id}"), Scope("write:lists")]
+		public async Task<IActionResult> Update(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			var title = Params.Get("title")?.Trim();
+			var policy = Params.Get("replies_policy");
+			if (title != default)
+			{
+				if (title.Length == 0 || title.Length > 200)
+					return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Title can't be blank");
+				list.Title = title;
+			}
+			if (policy != default)
+			{
+				if (!ListRepliesPolicy.IsValid(policy))
+					return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Replies policy is not included in the list");
+				list.RepliesPolicy = policy;
+			}
+			if (Params.Bool("exclusive") is { } exclusive)
+				list.Exclusive = exclusive;
+			await DB.Default.SaveAsync(list, token);
+			return Json(View(list));
+		}
+
+		[HttpDelete("/api/v1/lists/{id}"), Scope("write:lists")]
+		public async Task<IActionResult> Delete(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			await DB.Default.DeleteAsync<PersonaListMember>(m => m.ListId == list.ID);
+			await DB.Default.DeleteAsync<PersonaList>(list.ID);
+			return Json(new { });
+		}
+
+		[HttpGet("/api/v1/lists/{id}/accounts"), Scope("read:lists")]
+		public async Task<IActionResult> Accounts(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			await Members(list, token);
+			var members = await Page.From(Params, Limit(40, 80)).Fetch(DB.Default.Find<PersonaListMember>().Match(m => m.ListId == list.ID), m => m.ID, token);
+			var accounts = await _mapper.Accounts(members.Select(m => m.AccountId), token);
+			Link($"/api/v1/lists/{id}/accounts", members.LastOrDefault()?.ID, members.FirstOrDefault()?.ID);
+			return Json(members.Where(m => accounts.ContainsKey(m.AccountId)).Select(m => accounts[m.AccountId]).ToList());
+		}
+
+		// only accounts the persona follows may join its list, as on Mastodon
+		[HttpPost("/api/v1/lists/{id}/accounts"), Scope("write:lists")]
+		public async Task<IActionResult> Add(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			var ids = Params.List("account_ids").Distinct().ToList();
+			if (ids.Count == 0)
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Account ids can't be blank");
+			var followed = (await _dbEntities.Followings.Match(f => f.AvatarId == MyId && f.State == FollowState.Accepted && ids.Contains(f.TargetAccountId))
+				.ExecuteAsync(token)).Select(f => f.TargetAccountId).ToHashSet();
+			if (ids.Any(a => !followed.Contains(a)))
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: You must follow this account to add it to a list");
+			var present = (await DB.Default.Find<PersonaListMember>().Match(m => m.ListId == list.ID && ids.Contains(m.AccountId)).ExecuteAsync(token))
+				.Select(m => m.AccountId).ToHashSet();
+			if (await DB.Default.CountAsync<PersonaListMember>(m => m.ListId == list.ID, token) + ids.Count(a => !present.Contains(a)) > MaxMembers)
+				return Error(StatusCodes.Status422UnprocessableEntity, "Validation failed: Too many accounts in the list");
+			foreach (var account in ids.Where(a => !present.Contains(a)))
+				await DB.Default.SaveAsync(new PersonaListMember { ListId = list.ID, AvatarId = MyId, AccountId = account }, token);
+			return Json(new { });
+		}
+
+		[HttpDelete("/api/v1/lists/{id}/accounts"), Scope("write:lists")]
+		public async Task<IActionResult> Remove(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			var ids = Params.List("account_ids");
+			await DB.Default.DeleteAsync<PersonaListMember>(m => m.ListId == list.ID && ids.Contains(m.AccountId));
+			return Json(new { });
+		}
+
+		[HttpGet("/api/v1/accounts/{id}/lists"), Scope("read:lists")]
+		public async Task<IActionResult> Containing(string id, CancellationToken token)
+		{
+			var listIds = (await DB.Default.Find<PersonaListMember>().Match(m => m.AvatarId == MyId && m.AccountId == id).ExecuteAsync(token))
+				.Select(m => m.ListId).ToList();
+			return Json((await DB.Default.Find<PersonaList>().Match(l => l.AvatarId == MyId && listIds.Contains(l.ID)).ExecuteAsync(token))
+				.Select(View).ToList());
+		}
+
+		// the list's timeline: the persona's home entries by its members. Replies are kept as Mastodon keeps them: a member's
+		// replies to itself and to the persona always, to others as the policy says (anyone followed, the list's members, no one)
+		[HttpGet("/api/v1/timelines/list/{id}"), Scope("read:lists")]
+		public async Task<IActionResult> Timeline(string id, CancellationToken token)
+		{
+			if (await Mine(id, token) is not { } list)
+				return NotFoundError();
+			var members = await Members(list, token);
+			var entries = await Page.From(Params, Limit()).Fetch(
+				_dbEntities.TimelineEntries.Match(e => e.AvatarId == MyId && members.Contains(e.AuthorAccountId)), e => e.PostId, token);
+			var ids = entries.Select(e => e.PostId).ToList();
+			var posts = (await _dbEntities.Posts.Match(p => ids.Contains(p.ID)).Match(VisibilityPolicy.IsShown).ExecuteAsync(token)).ToDictionary(p => p.ID);
+			var answered = list.RepliesPolicy switch
+			{
+				ListRepliesPolicy.Followed => (await _dbEntities.Followings.Match(f => f.AvatarId == MyId && f.State == FollowState.Accepted).ExecuteAsync(token))
+					.Select(f => f.TargetAccountId).Append(MyId).ToHashSet(),
+				ListRepliesPolicy.List => members.Append(MyId).ToHashSet(),
+				_ => new HashSet<string> { MyId }
+			};
+			var shown = ids.Where(posts.ContainsKey).Select(i => posts[i])
+				.Where(p => p.ReblogOfPostId != default || string.IsNullOrEmpty(p.AnsweringToPostId) && string.IsNullOrEmpty(p.InReplyToURI)
+					|| p.InReplyToAccountId != default && (p.InReplyToAccountId == p.AuthorAccountId || answered.Contains(p.InReplyToAccountId)))
+				.ToList();
+			Link($"/api/v1/timelines/list/{id}", entries.LastOrDefault()?.PostId, entries.FirstOrDefault()?.PostId);
+			return Json(await _mapper.Statuses(shown, MyId, token));
+		}
+	}
+}

PrivaPub/Api/Mastodon/Controllers/SearchController.cs

@@ -90,9 +90,6 @@ namespace PrivaPub.Api.Mastodon.Controllers
 		[HttpGet("/api/v2/filters"), Scope("read:filters")]
 		public IActionResult FiltersV2() => Json(Array.Empty<object>());
 
-		[HttpGet("/api/v1/lists"), Scope("read:lists")]
-		public IActionResult Lists() => Json(Array.Empty<object>());
-
 		[HttpGet("/api/v1/announcements"), Microsoft.AspNetCore.Authorization.AllowAnonymous]
 		public IActionResult Announcements() => Json(Array.Empty<object>());
 

PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs

@@ -30,7 +30,15 @@ namespace PrivaPub.Api.Mastodon.Controllers
 		[HttpGet("/api/v1/timelines/home"), Scope("read:statuses")]
 		public async Task<IActionResult> Home(CancellationToken token)
 		{
-			var entries = await Page.From(Params, Limit()).Fetch(_dbEntities.TimelineEntries.Match(e => e.AvatarId == MyId), e => e.PostId, token);
+			//an exclusive list's members are read in that list, not at home
+			var exclusive = (await DB.Default.Find<PersonaList>().Match(l => l.AvatarId == MyId && l.Exclusive).ExecuteAsync(token)).Select(l => l.ID).ToList();
+			var apart = exclusive.Count == 0
+				? new List<string>()
+				: (await DB.Default.Find<PersonaListMember>().Match(m => exclusive.Contains(m.ListId)).ExecuteAsync(token)).Select(m => m.AccountId).Distinct().ToList();
+			var home = _dbEntities.TimelineEntries.Match(e => e.AvatarId == MyId);
+			if (apart.Count > 0)
+				home.Match(e => !apart.Contains(e.AuthorAccountId));
+			var entries = await Page.From(Params, Limit()).Fetch(home, e => e.PostId, token);
 			var ids = entries.Select(e => e.PostId).ToList();
 			var posts = (await _dbEntities.Posts.Match(p => ids.Contains(p.ID)).Match(VisibilityPolicy.IsShown).ExecuteAsync(token)).ToDictionary(p => p.ID);
 			var statuses = await _mapper.Statuses(ids.Where(posts.ContainsKey).Select(id => posts[id]).ToList(), MyId, token);
@@ -61,9 +69,6 @@ namespace PrivaPub.Api.Mastodon.Controllers
 			return await Respond(query, $"/api/v1/timelines/tag/{hashtag}", token);
 		}
 
-		[HttpGet("/api/v1/timelines/list/{id}"), Scope("read:lists")]
-		public IActionResult List(string id) => Json(Array.Empty<Status>());
-
 		[HttpGet("/api/v1/favourites"), Scope("read:favourites")]
 		public async Task<IActionResult> Favourites(CancellationToken token)
 		{

PrivaPub/Domain/Social/FollowService.cs

@@ -128,6 +128,8 @@ namespace PrivaPub.Domain.Social
 			{
 				return await _dbEntities.Followings.Match(f => f.AvatarId == follower.Id && f.TargetActorURI == targetUri).ExecuteFirstAsync(token);
 			}
+			//a new follow starts in no list, whatever lists the account was in before a follow that ended without passing here
+			await DB.Default.DeleteAsync<PersonaListMember>(m => m.AvatarId == follower.Id && m.AccountId == following.TargetAccountId);
 
 			if (local != default)
 				await FollowLocally(follower, local, following, token);
@@ -145,6 +147,7 @@ namespace PrivaPub.Domain.Social
 				return;
 
 			await DB.Default.DeleteAsync<Following>(following.ID);
+			await DB.Default.DeleteAsync<PersonaListMember>(m => m.AvatarId == follower.Id && m.AccountId == following.TargetAccountId);
 			if (following.TargetIsLocal)
 			{
 				await DB.Default.DeleteAsync<Follower>(f => f.LocalActorId == following.TargetAccountId && f.ActorURI == follower.Uri);

PrivaPub/Infrastructure/Data/Indexes.cs

@@ -95,6 +95,7 @@ namespace PrivaPub.Infrastructure.Data
 			foreach (var pair in new (Func<Task>, string)[]
 			{
 				(() => DB.Default.Index<Block>().Key(b => b.AvatarId, KeyType.Ascending).Key(b => b.TargetActorURI, KeyType.Ascending).Option(o => o.Unique = true).CreateAsync(token), "block"),
+				(() => DB.Default.Index<PersonaListMember>().Key(m => m.ListId, KeyType.Ascending).Key(m => m.AccountId, KeyType.Ascending).Option(o => o.Unique = true).CreateAsync(token), "list member"),
 				(() => DB.Default.Index<BlockedBy>().Key(b => b.AvatarId, KeyType.Ascending).Key(b => b.ActorURI, KeyType.Ascending).Option(o => o.Unique = true).CreateAsync(token), "blocked by"),
 				(() => DB.Default.Index<Mute>().Key(m => m.AvatarId, KeyType.Ascending).Key(m => m.TargetActorURI, KeyType.Ascending).Option(o => o.Unique = true).CreateAsync(token), "mute"),
 				(() => DB.Default.Index<AccountDomainBlock>().Key(b => b.AvatarId, KeyType.Ascending).Key(b => b.Domain, KeyType.Ascending).Option(o => o.Unique = true).CreateAsync(token), "domain block"),
@@ -104,6 +105,8 @@ namespace PrivaPub.Infrastructure.Data
 				await pair.Item1();
 			await Plain<Block>(token, b => b.TargetActorURI);
 			await Plain<BlockedBy>(token, b => b.ActorURI);
+			await Plain<PersonaList>(token, l => l.AvatarId);
+			await Plain<PersonaListMember>(token, m => m.AvatarId);
 			await Plain<Mute>(token, m => m.TargetActorURI);
 			await Plain<Report>(token, r => r.IsResolved, r => r.ID);
 			await Unique<DomainBlock>(b => b.Domain, Builders<DomainBlock>.Filter.Type(b => b.Domain, BsonType.String), token);

PrivaPub/Models/Social/Lists.cs

@@ -0,0 +1,32 @@
+using MongoDB.Entities;
+
+namespace PrivaPub.Models.Social
+{
+	//a persona's list of accounts it follows (Mastodon lists): a timeline of their posts, and, when exclusive, their posts
+	//kept out of the home timeline. Lists are the persona's own and never federate.
+	public class PersonaList : Entity
+	{
+		public string AvatarId { get; set; }
+		public string Title { get; set; }
+		public string RepliesPolicy { get; set; } = ListRepliesPolicy.List;
+		public bool Exclusive { get; set; }
+		public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+	}
+
+	public class PersonaListMember : Entity
+	{
+		public string ListId { get; set; }
+		public string AvatarId { get; set; }//the list's owner
+		public string AccountId { get; set; }//the member: a ForeignAvatar.ID, an Avatar.ID or a community's Group.ID
+		public DateTime AddedAt { get; set; } = DateTime.UtcNow;
+	}
+
+	public static class ListRepliesPolicy
+	{
+		public const string Followed = "followed";//replies to anyone the persona follows
+		public const string List = "list";//replies to members of the list
+		public const string None = "none";
+
+		public static bool IsValid(string value) => value is Followed or List or None;
+	}
+}

PrivaPub/Services/RootRemoval.cs

@@ -62,6 +62,8 @@ namespace PrivaPub.Services
 				await Announce(persona, followed, token);
 				await DB.Default.Update<Avatar>().MatchID(avatar.ID).Modify(a => a.DeletionAt, now).ExecuteAsync(token);
 				await Empty(avatar.ID, now, token);
+				await DB.Default.DeleteAsync<Models.Social.PersonaListMember>(m => m.AvatarId == avatar.ID);
+				await DB.Default.DeleteAsync<Models.Social.PersonaList>(l => l.AvatarId == avatar.ID);
 			}
 
 			await DB.Default.Update<RootUser>().MatchID(root.ID)