fix(#253 PR2): close review findings (ETag/items consistency + SPA load ordering)

Independent Codex review of #268 found two Blockers the fork missed + two Mediums:
- Blocker: replace PUTs returned the handler's item snapshot but re-queried the root
  for the ETag separately, so a racing writer could pair stale items with a newer ETag
  (silent overwrite). All four controllers now reload root-then-items (version-first,
  fail-safe) and 404 when the root is gone between commit and reload — matching the
  Block reference. Fixes the Blocker + the Medium '200 without ETag' case together.
- Blocker: PlaylistsScreen loaded items+root via Promise.all (concurrent), pairing a
  stale name with the current ETag; now sequential (items-with-meta first, then root).
- Medium: SchedulesScreen loadItems now marks not-loaded/loading up front so canEdit is
  false through the 412 conflict reload (no stale-draft edits lost).

Controller unit-test mocks updated to stub the new reload query. Full suite green
(ErsatzTV.Tests 1334, web 667, check:api no drift).

ErsatzTV/Controllers/Api/DecoTemplateController.cs

@@ -212,10 +212,14 @@ public class DecoTemplateController(IMediator mediator) : ControllerBase
 
         return await result.Match(
             Left: error => Task.FromResult(error.ToErrorResult()),
-            Right: async items =>
+            Right: async _ =>
             {
+                // Reload the root (version) FIRST, then the items, so the emitted ETag is never newer than
+                // the returned items (issue #253 fail-safe ordering; matches BlockController).
                 Option<DecoTemplateViewModel> refreshed =
                     await mediator.Send(new GetDecoTemplateById(id), cancellationToken);
+                List<DecoTemplateItemViewModel> items =
+                    await mediator.Send(new GetDecoTemplateItems(id), cancellationToken);
                 return refreshed.Match(
                     Some: vm =>
                     {

ErsatzTV/Controllers/Api/PlaylistController.cs

@@ -222,12 +222,21 @@ public class PlaylistController(IMediator mediator) : ControllerBase
             await mediator.Send(request.ToCommand(id, ifMatch.ExpectedVersion), cancellationToken);
         return await result.Match(
             Left: error => Task.FromResult(error.ToErrorResult()),
-            Right: async items =>
+            Right: async _ =>
             {
+                // Reload the root (version) FIRST, then the items, so the emitted ETag is never newer than
+                // the returned items (issue #253 fail-safe ordering; matches BlockController). A None root
+                // (deleted between commit and reload) is a 404, never a 200 without an ETag.
                 Option<PlaylistViewModel> refreshed =
                     await mediator.Send(new GetPlaylistById(id), cancellationToken);
-                refreshed.Do(vm => ConcurrencyHeaders.SetETag(Response, vm.Version));
-                return (IActionResult)new OkObjectResult(items.Map(ProjectToItemResponse).ToList());
+                List<PlaylistItemViewModel> items = await mediator.Send(new GetPlaylistItems(id), cancellationToken);
+                return refreshed.Match(
+                    Some: vm =>
+                    {
+                        ConcurrencyHeaders.SetETag(Response, vm.Version);
+                        return (IActionResult)new OkObjectResult(items.Map(ProjectToItemResponse).ToList());
+                    },
+                    None: () => ApiResults.NotFoundProblem());
             });
     }
 

ErsatzTV/Controllers/Api/ScheduleController.cs

@@ -180,15 +180,24 @@ public class ScheduleController(IMediator mediator) : ControllerBase
 
         return await result.Match(
             Left: error => Task.FromResult(error.ToErrorResult()),
-            Right: async items =>
+            Right: async _ =>
             {
-                // Return the new ETag so a same-tab second save doesn't 412 against its own write.
+                // Reload the root (version) FIRST, then the items, so the emitted ETag is never newer than
+                // the returned items (issue #253 fail-safe ordering; matches BlockController). A None root
+                // (deleted between commit and reload) is a 404, never a 200 without an ETag.
                 Option<ProgramScheduleViewModel> refreshed =
                     await mediator.Send(new GetProgramScheduleById(id), cancellationToken);
-                refreshed.IfSome(vm => ConcurrencyHeaders.SetETag(Response, vm.Version));
-
-                return (IActionResult)new OkObjectResult(
-                    items.Select(ScheduleItemResponseMapper.ProjectToResponseModel).ToList());
+                List<ProgramScheduleItemViewModel> items =
+                    await mediator.Send(new GetProgramScheduleItems(id), cancellationToken);
+                return refreshed.Match(
+                    Some: vm =>
+                    {
+                        // Return the new ETag so a same-tab second save doesn't 412 against its own write.
+                        ConcurrencyHeaders.SetETag(Response, vm.Version);
+                        return (IActionResult)new OkObjectResult(
+                            items.Select(ScheduleItemResponseMapper.ProjectToResponseModel).ToList());
+                    },
+                    None: () => ApiResults.NotFoundProblem());
             });
     }
 

ErsatzTV/Controllers/Api/TemplateController.cs

@@ -200,9 +200,14 @@ public class TemplateController(IMediator mediator) : ControllerBase
 
         return await result.Match(
             Left: error => Task.FromResult(error.ToErrorResult()),
-            Right: async items =>
+            Right: async _ =>
             {
+                // Reload the root (version) FIRST, then the items, so the emitted ETag is never newer than
+                // the returned items (issue #253 fail-safe ordering; matches BlockController). Returning the
+                // handler's item snapshot alongside a separately re-queried version could pair stale items
+                // with a newer ETag — a client would then silently overwrite the interleaving write.
                 Option<TemplateViewModel> refreshed = await mediator.Send(new GetTemplateById(id), cancellationToken);
+                List<TemplateItemViewModel> items = await mediator.Send(new GetTemplateItems(id), cancellationToken);
                 return refreshed.Match(
                     Some: vm =>
                     {