fix(#193): review follow-ups — drop Playlist option, non-tracking existence check

Adversarial review follow-ups on the #193 rerun selection validation:
- RerunCollectionEditor.razor: remove the CollectionType.Playlist
  dropdown option — RerunCollection has no PlaylistId column, so the
  option previously persisted a broken row and now fails validation.
- RerunCollectionSelectionValidation: replace FindAsync with a
  non-tracking AnyAsync(EF.Property<int>("Id") == id) existence check
  so nothing is materialized/tracked into the save-path context.
- Tests: pin the deliberate 422-not-404 choice
  (ShouldNotBeOfType<NotFoundError>) and cover the unsupported-type
  default arm (Playlist -> "Unsupported collection type"), which was
  reachable via the Blazor editor.

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

ErsatzTV.Application/MediaCollections/Commands/RerunCollectionSelectionValidation.cs

@@ -100,7 +100,9 @@ internal static class RerunCollectionSelectionValidation
         CancellationToken cancellationToken)
         where T : class
     {
-        if (id is null || await set.FindAsync([id.Value], cancellationToken) is null)
+        // pure existence check — no tracking, nothing materialized into the save-path context
+        if (id is null ||
+            !await set.AnyAsync(e => EF.Property<int>(e, "Id") == id.Value, cancellationToken))
         {
             return Fail<BaseError, Unit>(errorMessage);
         }

ErsatzTV.Tests/Application/MediaCollections/RerunCollectionHandlerTests.cs

@@ -3,6 +3,7 @@ using ErsatzTV.Application.MediaCollections;
 using ErsatzTV.Application.MediaItems;
 using ErsatzTV.Core;
 using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Errors;
 using ErsatzTV.Core.Interfaces.Repositories;
 using ErsatzTV.Infrastructure.Data;
 using ErsatzTV.Tests.Support;
@@ -32,9 +33,25 @@ public class RerunCollectionHandlerTests : MediaCollectionHandlerTestBase
             CancellationToken.None);
 
         BaseError error = LeftOf(result);
+        // deliberate 422-not-404: the missing entity is a request-body FK, not the route resource
+        error.ShouldNotBeOfType<NotFoundError>();
         error.Value.ShouldContain("Collection does not exist");
     }
 
+    [Test]
+    public async Task Create_Should_Return_Error_When_CollectionType_Unsupported()
+    {
+        var handler = new CreateRerunCollectionHandler(Db.Factory);
+
+        // reachable via the legacy Blazor editor (no IsSupportedSelectionType pre-check)
+        Either<BaseError, RerunCollectionViewModel> result = await handler.Handle(
+            MakeCreate(CollectionType.Playlist),
+            CancellationToken.None);
+
+        BaseError error = LeftOf(result);
+        error.Value.ShouldContain("Unsupported collection type");
+    }
+
     [Test]
     public async Task Create_Should_Return_Error_When_MediaItem_Missing()
     {

ErsatzTV/Pages/RerunCollectionEditor.razor

@@ -36,7 +36,6 @@
                     <MudSelectItem Value="CollectionType.Artist">Artist</MudSelectItem>
                     <MudSelectItem Value="CollectionType.MultiCollection">Multi Collection</MudSelectItem>
                     <MudSelectItem Value="CollectionType.SmartCollection">Smart Collection</MudSelectItem>
-                    <MudSelectItem Value="CollectionType.Playlist">Playlist</MudSelectItem>
                 </MudSelect>
             </MudStack>
             @if (_model.CollectionType == CollectionType.Collection)