feat(api): add channel state endpoint contract

ErsatzTV.Application/Channels/Queries/GetChannelStatesForApi.cs

@@ -0,0 +1,5 @@
+using ErsatzTV.Core.Api.Channels;
+
+namespace ErsatzTV.Application.Channels;
+
+public record GetChannelStatesForApi : IRequest<List<ChannelStateResponseModel>>;

ErsatzTV.Core/Api/Channels/ChannelNowPlayingResponseModel.cs

@@ -0,0 +1,6 @@
+namespace ErsatzTV.Core.Api.Channels;
+
+public record ChannelNowPlayingResponseModel(
+    string Title,
+    DateTimeOffset StartUtc,
+    DateTimeOffset FinishUtc);

ErsatzTV.Core/Api/Channels/ChannelStateResponseModel.cs

@@ -0,0 +1,7 @@
+namespace ErsatzTV.Core.Api.Channels;
+
+public record ChannelStateResponseModel(
+    int ChannelId,
+    string ChannelNumber,
+    bool OnAir,
+    ChannelNowPlayingResponseModel NowPlaying);

ErsatzTV.Tests/Controllers/ChannelControllerTests.cs

@@ -6,6 +6,7 @@ using ErsatzTV.Application.Playouts;
 using ErsatzTV.Controllers.Api;
 using ErsatzTV.Controllers.Api.Requests;
 using ErsatzTV.Core;
+using ErsatzTV.Core.Api.Channels;
 using ErsatzTV.Core.Domain;
 using ErsatzTV.Core.Errors;
 using LanguageExt;
@@ -34,6 +35,25 @@ public class ChannelControllerTests
         _controller = new ChannelController(writer, _mediator);
     }
 
+    [Test]
+    public async Task GetState_Should_Return_200_With_Channel_State()
+    {
+        var state = new ChannelStateResponseModel(
+            7,
+            "7.1",
+            true,
+            new ChannelNowPlayingResponseModel(
+                "Retro Cartoons",
+                new DateTimeOffset(2026, 7, 2, 17, 0, 0, TimeSpan.Zero),
+                new DateTimeOffset(2026, 7, 2, 17, 30, 0, TimeSpan.Zero)));
+        _mediator.Send(Arg.Any<GetChannelStatesForApi>(), Arg.Any<CancellationToken>())
+            .Returns([state]);
+
+        IActionResult result = await _controller.GetState(CancellationToken.None);
+
+        result.ShouldBeOfType<OkObjectResult>().Value.ShouldBe(new List<ChannelStateResponseModel> { state });
+    }
+
     [Test]
     public async Task Create_Should_Return_201_With_Location_And_Body()
     {

ErsatzTV/Controllers/Api/ChannelController.cs

@@ -21,6 +21,18 @@ public class ChannelController(ChannelWriter<IBackgroundServiceRequest> workerCh
     [EndpointGroupName("general")]
     public async Task<List<ChannelResponseModel>> GetAll() => await mediator.Send(new GetAllChannelsForApi());
 
+    [HttpGet("/api/channels/state")]
+    [Tags("Channels")]
+    [EndpointSummary("Get channel runtime state")]
+    [EndpointGroupName("general")]
+    [ProducesResponseType(typeof(List<ChannelStateResponseModel>), StatusCodes.Status200OK)]
+    public async Task<IActionResult> GetState(CancellationToken cancellationToken)
+    {
+        List<ChannelStateResponseModel> result =
+            await mediator.Send(new GetChannelStatesForApi(), cancellationToken);
+        return new OkObjectResult(result);
+    }
+
     [HttpGet("/api/channels/{id:int}", Name = "GetChannelById")]
     [Tags("Channels")]
     [EndpointSummary("Get a channel by id")]