8.3 Wrap full pipeline in lock

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

IMPLEMENTATION.md

@@ -202,7 +202,7 @@ Each type lives in `src/FrameProcessor/Domain/`. Tests in `tests/FrameProcessor.
 - `ConcurrentDictionary<FrameName, SemaphoreSlim>` (each `SemaphoreSlim(1, 1)`).
 - `Task<IDisposable> AcquireAsync(FrameName, CancellationToken)` returning a disposable that releases on dispose.
 
-### [ ] 8.3 Wrap full pipeline in lock
+### [x] 8.3 Wrap full pipeline in lock
 - In `FramesController`, acquire the frame's lock before fetch/decode and release after publish-attempt completes (`CLAUDE.md` "Per-frame serialization").
 - **Manual check:** fire two concurrent uploads to the same frame → both return 200, only one PNG on disk reflects whichever finished last, two MQTT publishes (or one if collapsed by retry queue).
 

src/FrameProcessor/Controllers/FramesController.cs

@@ -1,3 +1,4 @@
+using FrameProcessor.Concurrency;
 using FrameProcessor.Configuration;
 using FrameProcessor.Domain;
 using FrameProcessor.ImagePipeline;
@@ -17,19 +18,22 @@ public sealed class FramesController : ControllerBase
     private readonly ImageStore _store;
     private readonly MqttPublisher _mqtt;
     private readonly IImageUrlFetcher _urlFetcher;
+    private readonly FrameLockProvider _locks;
 
     public FramesController(
         FramesRegistry frames,
         IImagePipeline pipeline,
         ImageStore store,
         MqttPublisher mqtt,
-        IImageUrlFetcher urlFetcher)
+        IImageUrlFetcher urlFetcher,
+        FrameLockProvider locks)
     {
         _frames = frames;
         _pipeline = pipeline;
         _store = store;
         _mqtt = mqtt;
         _urlFetcher = urlFetcher;
+        _locks = locks;
     }
 
     [HttpPost("{name}/image")]
@@ -46,6 +50,8 @@ public sealed class FramesController : ControllerBase
             return BadRequest(new { error = "Missing 'image' file part." });
         }
 
+        using (await _locks.AcquireAsync(frame.Name, cancellationToken).ConfigureAwait(false))
+        {
             byte[] pngBytes;
             await using (var stream = file.OpenReadStream())
             {
@@ -54,6 +60,7 @@ public sealed class FramesController : ControllerBase
 
             return await FinishUploadAsync(frame, pngBytes, cancellationToken).ConfigureAwait(false);
         }
+    }
 
     [HttpPost("{name}/image-url")]
     public async Task<IActionResult> UploadImageUrl(
@@ -73,6 +80,8 @@ public sealed class FramesController : ControllerBase
             return BadRequest(new { error = "Missing or invalid 'url'." });
         }
 
+        using (await _locks.AcquireAsync(frame.Name, cancellationToken).ConfigureAwait(false))
+        {
             Stream source;
             try
             {
@@ -91,6 +100,7 @@ public sealed class FramesController : ControllerBase
 
             return await FinishUploadAsync(frame, pngBytes, cancellationToken).ConfigureAwait(false);
         }
+    }
 
     private async Task<IActionResult> FinishUploadAsync(Frame frame, byte[] pngBytes, CancellationToken cancellationToken)
     {

src/FrameProcessor/Program.cs

@@ -1,3 +1,4 @@
+using FrameProcessor.Concurrency;
 using FrameProcessor.Configuration;
 using FrameProcessor.ImagePipeline;
 using FrameProcessor.Middleware;
@@ -44,6 +45,7 @@ builder.Services.AddSingleton<IImagePipeline, FrameProcessor.ImagePipeline.Image
 builder.Services.AddSingleton<ImageStore>();
 builder.Services.AddSingleton<MqttPublisher>();
 builder.Services.AddHostedService(sp => sp.GetRequiredService<MqttPublisher>());
+builder.Services.AddSingleton<FrameLockProvider>();
 
 builder.Services.AddHttpClient<IImageUrlFetcher, ImageUrlFetcher>((sp, client) =>
 {