feat(235): async-op API contract normalization — playouts slice C (#235)

Slice C of the async-op contract normalization:

- channel reset (POST /api/channels/{channelNumber}/playout/reset) now
  returns 202 Accepted (was 200 Ok) — it only queues a background rebuild
- reset-all (POST /api/playouts/reset-all) still 202 but now returns a
  ResetAllPlayoutsResponseModel body reporting QueuedPlayoutIds /
  SkippedLocked / SkippedUnsupported instead of silently swallowing skips;
  handler returns a new ResetAllPlayoutsResult record
- single-playout GET (GET /api/playouts/{id}) now exposes IsLocked on
  PlayoutResponseModel, set from IEntityLocker.IsPlayoutLocked mirroring
  the list projection — gives a polling client the lock flag

Tests: channel reset asserts 202; reset-all asserts 202 + skipped-body
shape; single GET asserts IsLocked; new ResetAllPlayoutsHandlerTests
(in-memory SQLite) asserts locked/ExternalJson/None land in skipped lists
and eligible playouts in queued. docs/api-conventions.md §3a updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ErsatzTV/Controllers/Api/ChannelController.cs

@@ -211,7 +211,7 @@ public class ChannelController(
         "progress) and all other playout kinds use Reset (rebuild from scratch), matching the Blazor UI. " +
         "Pass mode to force a specific PlayoutBuildMode.")]
     [EndpointGroupName("general")]
-    [ProducesResponseType(StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status202Accepted)]
     [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
     [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status409Conflict)]
     public async Task<IActionResult> ResetPlayout(
@@ -233,7 +233,7 @@ public class ChannelController(
 
             PlayoutBuildMode buildMode = mode ?? await DefaultResetMode(playoutId, cancellationToken);
             await workerChannel.WriteAsync(new BuildPlayout(playoutId, buildMode), cancellationToken);
-            return new OkResult();
+            return new AcceptedResult();
         }
 
         return ApiResults.NotFoundProblem();

ErsatzTV/Controllers/Api/PlayoutController.cs

@@ -69,7 +69,7 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
     public async Task<IActionResult> GetById(int id, CancellationToken cancellationToken)
     {
         Option<PlayoutNameViewModel> result = await mediator.Send(new GetPlayoutById(id), cancellationToken);
-        return result.Map(ToResponse).ToGetResult();
+        return result.Map(vm => ToResponse(vm, entityLocker.IsPlayoutLocked(id))).ToGetResult();
     }
 
     [HttpGet("/api/playouts/{id:int}/items", Name = "GetPlayoutItems")]
@@ -128,7 +128,9 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
                         Option<PlayoutNameViewModel> playout =
                             await mediator.Send(new GetPlayoutById(created.PlayoutId), cancellationToken);
                         return playout.Match(
-                            Some: vm => (IActionResult)new CreatedResult($"/api/playouts/{vm.PlayoutId}", ToResponse(vm)),
+                            Some: vm => (IActionResult)new CreatedResult(
+                                $"/api/playouts/{vm.PlayoutId}",
+                                ToResponse(vm, entityLocker.IsPlayoutLocked(vm.PlayoutId))),
                             None: () => ApiResults.NotFoundProblem());
                     });
             });
@@ -194,7 +196,8 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
 
         return result.Match(
             Left: error => error.ToErrorResult(),
-            Right: playout => (IActionResult)new OkObjectResult(ToResponse(playout)));
+            Right: playout => (IActionResult)new OkObjectResult(
+                ToResponse(playout, entityLocker.IsPlayoutLocked(id))));
     }
 
     private async Task<Either<BaseError, PlayoutNameViewModel>> UpdateScheduleFile(
@@ -260,7 +263,7 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
 
         Option<PlayoutNameViewModel> refreshed = await mediator.Send(new GetPlayoutById(id), cancellationToken);
         return refreshed.Match(
-            Some: vm => (IActionResult)new OkObjectResult(ToResponse(vm)),
+            Some: vm => (IActionResult)new OkObjectResult(ToResponse(vm, entityLocker.IsPlayoutLocked(id))),
             None: () => ApiResults.NotFoundProblem());
     }
 
@@ -550,14 +553,19 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
     [Tags("Playouts")]
     [EndpointSummary("Reset all playouts")]
     [EndpointGroupName("general")]
-    [ProducesResponseType(StatusCodes.Status202Accepted)]
+    [ProducesResponseType(typeof(ResetAllPlayoutsResponseModel), StatusCodes.Status202Accepted)]
     // No 409 lock guard here (unlike the id-keyed mutations): ResetAllPlayoutsHandler already
     // skips any playout whose build lock is held, matching Blazor. It is a fire-and-forget
-    // bulk enqueue, so it always accepts. See docs/decisions.md 2026-07-10.
+    // bulk enqueue, so it always accepts — the 202 body reports which playouts were queued and
+    // which were skipped (locked, or an unsupported ExternalJson/None kind). See docs/decisions.md 2026-07-10.
     public async Task<IActionResult> ResetAll(CancellationToken cancellationToken)
     {
-        await mediator.Send(new ResetAllPlayouts(), cancellationToken);
-        return Accepted();
+        ResetAllPlayoutsResult result = await mediator.Send(new ResetAllPlayouts(), cancellationToken);
+        var body = new ResetAllPlayoutsResponseModel(
+            result.QueuedPlayoutIds,
+            result.SkippedLocked,
+            result.SkippedUnsupported);
+        return new AcceptedResult((string)null, body);
     }
 
     [HttpPost("/api/playouts/{id:int}/erase-items", Name = "ErasePlayoutItems")]
@@ -728,7 +736,7 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
     private static PlayoutHistoryDetailsResponseModel ToDetailsResponse(PlayoutHistoryDetailsViewModel vm) =>
         new(vm.PlaybackOrder, vm.CollectionType, vm.Name, vm.MediaItemType, vm.MediaItemTitle);
 
-    private static PlayoutResponseModel ToResponse(PlayoutNameViewModel vm) =>
+    private static PlayoutResponseModel ToResponse(PlayoutNameViewModel vm, bool isLocked) =>
         PlayoutResponseModel.From(
             vm.PlayoutId,
             vm.ScheduleKind,
@@ -740,7 +748,8 @@ public class PlayoutController(IMediator mediator, IEntityLocker entityLocker) :
             vm.DbDailyRebuildTime,
             ToBuildStatus(vm.BuildStatus),
             vm.DecoId,
-            vm.DecoName);
+            vm.DecoName,
+            isLocked);
 
     private static PlayoutAlternateScheduleResponseModel ToResponse(PlayoutAlternateScheduleViewModel vm) =>
         new(