feat(lists): allow nested sidebar folders via drag and drop

Folders can now contain other folders, to arbitrary depth, via a
self-referencing parent_folder_id (ON DELETE SET NULL, same pattern as
lists.folder_id). Nesting/un-nesting is drag-and-drop only: dropping a
folder onto another folder's header middle moves it in, the outer
quarters or any top-level/in-folder drop insert it beside a target.
Dropping a folder into itself or one of its own subfolders is silently
ignored. Deleting a folder releases its lists and subfolders back to
the top level, unchanged from the existing list behavior.

ListFolderNavItemViewModel.Lists became Children (object, mixing lists
and subfolders, mirroring TopLevel) so the existing implicit, type-matched
DataTemplates render nested folders recursively without new XAML, and each
nesting level gets its indent for free from the folder template's own
margin. Folders/RootLists/ContainerOf/PersistOrderAsync/RecomputeFolderCounts
now walk the tree instead of assuming one level.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/ClaudeDo.Data/CLAUDE.md

@@ -14,7 +14,7 @@ Shared data layer: models, repositories, SQLite infrastructure, and git operatio
   - Legacy status values `Manual`/`Planning`/`Planned`/`Draft`/`Waiting` were retired. The backfill migration was squashed away (2026-08-26) — a database still holding those values can't be upgraded, see Schema below.
 - **ListEntity** — Id, Name, WorkingDir, DefaultCommitType, CreatedAt, IsManual (reminder list — tasks created here default to `IsManual`), Icon, FolderId
   - `FolderId` (`folder_id`, nullable FK → `list_folders.id`, `ON DELETE SET NULL`) — the sidebar folder the list sits in; null = top level. Written only by the UI (`ListsIslandViewModel` drag/context menu), never by MCP.
-- **ListFolderEntity** — Id, Name, Icon, SortOrder, IsCollapsed, CreatedAt → `list_folders`. A pure sidebar grouping: no tasks, no config, no working dir, **one level** (folders never nest). Deliberately its own table rather than a flag on `lists`, so every caller that enumerates lists (MCP `list_task_lists`, "move to list", the queue picker, repo import) needs no folder filtering. Folder CRUD lives on `ListRepository`.
+- **ListFolderEntity** — Id, Name, Icon, SortOrder, IsCollapsed, ParentFolderId, CreatedAt → `list_folders`. A pure sidebar grouping: no tasks, no config, no working dir. `ParentFolderId` (self-FK, `ON DELETE SET NULL`) lets folders nest arbitrarily deep — drag-and-drop only, no UI to pick a parent otherwise. Deliberately its own table rather than a flag on `lists`, so every caller that enumerates lists (MCP `list_task_lists`, "move to list", the queue picker, repo import) needs no folder filtering. Folder CRUD lives on `ListRepository`.
 - **ListConfigEntity** — ListId (PK, 1:1), Model, SystemPrompt, AgentPath, MaxTurns, SessionSkills, VerifyCommand, PermissionMode, TicketProjectId (all nullable). `VerifyCommand` is an optional post-merge gate; null/blank = no gate → [review-merge](../../docs/explore-notes/review-merge.md). `PermissionMode` is null = inherit the global default; resolution order task → list → global lives in `EffectiveRunConfigResolver`. `TicketProjectId` (`ticket_project_id`) links the list to a project in the external ticket system; null = not linked → `ClaudeDo.Worker/CLAUDE.md` Tickets section.
   - ⚠️ `ListRepository.SetConfigAsync` copies the entity **verbatim**, so every writer must carry the fields it doesn't own (`SessionSkills`, `PermissionMode`, `TicketProjectId`) or they silently reset. `UpdateListConfigDto.TicketProjectId` is tri-state (`null` = keep stored) for exactly that reason — only the list-settings modal sends an explicit value. This bit `PermissionMode` for real: its update-branch copy was missing from `SetConfigAsync` until `f0a3a186`, so a list's permission-mode override only ever stuck on the list's *first* save, never on a later one.
 - **WorktreeEntity** — TaskId (PK, 1:1), Path, BranchName, BaseCommit, HeadCommit, DiffStat, MergeCommit (nullable — SHA of the merge commit this branch produced; the only thing making `revert_merge` possible without searching `git log`), State (`Active|Merged|Discarded|Kept`)

src/ClaudeDo.Data/Configuration/ListFolderEntityConfiguration.cs

@@ -17,7 +17,14 @@ public class ListFolderEntityConfiguration : IEntityTypeConfiguration<ListFolder
         builder.Property(f => f.Icon).HasColumnName("icon");
         builder.Property(f => f.SortOrder).HasColumnName("sort_order").IsRequired().HasDefaultValue(0);
         builder.Property(f => f.IsCollapsed).HasColumnName("is_collapsed").IsRequired().HasDefaultValue(false);
+        builder.Property(f => f.ParentFolderId).HasColumnName("parent_folder_id");
 
         builder.HasIndex(f => f.SortOrder).HasDatabaseName("idx_list_folders_sort");
+        builder.HasIndex(f => f.ParentFolderId).HasDatabaseName("idx_list_folders_parent");
+
+        builder.HasOne<ListFolderEntity>()
+            .WithMany()
+            .HasForeignKey(f => f.ParentFolderId)
+            .OnDelete(DeleteBehavior.SetNull);
     }
 }

src/ClaudeDo.Data/Migrations/20260928111701_AddNestedListFolders.cs

@@ -0,0 +1,49 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ClaudeDo.Data.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddNestedListFolders : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "parent_folder_id",
+                table: "list_folders",
+                type: "TEXT",
+                nullable: true);
+
+            migrationBuilder.CreateIndex(
+                name: "idx_list_folders_parent",
+                table: "list_folders",
+                column: "parent_folder_id");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_list_folders_list_folders_parent_folder_id",
+                table: "list_folders",
+                column: "parent_folder_id",
+                principalTable: "list_folders",
+                principalColumn: "id",
+                onDelete: ReferentialAction.SetNull);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_list_folders_list_folders_parent_folder_id",
+                table: "list_folders");
+
+            migrationBuilder.DropIndex(
+                name: "idx_list_folders_parent",
+                table: "list_folders");
+
+            migrationBuilder.DropColumn(
+                name: "parent_folder_id",
+                table: "list_folders");
+        }
+    }
+}

src/ClaudeDo.Data/Migrations/ClaudeDoDbContextModelSnapshot.cs

@@ -389,6 +389,10 @@ namespace ClaudeDo.Data.Migrations
                         .HasColumnType("TEXT")
                         .HasColumnName("name");
 
+                    b.Property<string>("ParentFolderId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("parent_folder_id");
+
                     b.Property<int>("SortOrder")
                         .ValueGeneratedOnAdd()
                         .HasColumnType("INTEGER")
@@ -397,6 +401,9 @@ namespace ClaudeDo.Data.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("ParentFolderId")
+                        .HasDatabaseName("idx_list_folders_parent");
+
                     b.HasIndex("SortOrder")
                         .HasDatabaseName("idx_list_folders_sort");
 
@@ -1027,6 +1034,14 @@ namespace ClaudeDo.Data.Migrations
                         .OnDelete(DeleteBehavior.SetNull);
                 });
 
+            modelBuilder.Entity("ClaudeDo.Data.Models.ListFolderEntity", b =>
+                {
+                    b.HasOne("ClaudeDo.Data.Models.ListFolderEntity", null)
+                        .WithMany()
+                        .HasForeignKey("ParentFolderId")
+                        .OnDelete(DeleteBehavior.SetNull);
+                });
+
             modelBuilder.Entity("ClaudeDo.Data.Models.SubtaskEntity", b =>
                 {
                     b.HasOne("ClaudeDo.Data.Models.TaskEntity", "Task")

src/ClaudeDo.Data/Models/ListFolderEntity.cs

@@ -4,7 +4,7 @@ namespace ClaudeDo.Data.Models;
 /// A sidebar folder grouping user lists. Deliberately its own table rather than a flag on
 /// <see cref="ListEntity"/>: every place that enumerates lists (MCP list_task_lists, "move to
 /// list", the queue picker, repo import) would otherwise have to filter folders out.
-/// One level only — a folder holds lists, never other folders.
+/// Folders nest arbitrarily deep via <see cref="ParentFolderId"/>.
 /// </summary>
 public sealed class ListFolderEntity
 {
@@ -17,4 +17,7 @@ public sealed class ListFolderEntity
     // Sidebar expand/collapse state. Lives here rather than in ui.config.json because the row is
     // already being read for the folder itself.
     public bool IsCollapsed { get; set; }
+    // Parent folder, or null for a top-level folder. Self-FK, ON DELETE SET NULL — deleting a
+    // folder releases its subfolders to the top level, same as it does for its lists.
+    public string? ParentFolderId { get; set; }
 }

src/ClaudeDo.Data/Repositories/ListRepository.cs

@@ -135,6 +135,14 @@ public sealed class ListRepository
             .ExecuteUpdateAsync(s => s.SetProperty(f => f.IsCollapsed, collapsed), ct);
     }
 
+    /// <summary>Moves a folder under <paramref name="parentFolderId"/>, or to the top level when null.</summary>
+    public async Task SetFolderParentAsync(string folderId, string? parentFolderId, CancellationToken ct = default)
+    {
+        await _context.ListFolders
+            .Where(f => f.Id == folderId)
+            .ExecuteUpdateAsync(s => s.SetProperty(f => f.ParentFolderId, parentFolderId), ct);
+    }
+
     /// <summary>Moves a list into <paramref name="folderId"/>, or back to the top level when null.</summary>
     public async Task SetListFolderAsync(string listId, string? folderId, CancellationToken ct = default)
     {