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")]
@@ -46,13 +50,16 @@ public sealed class FramesController : ControllerBase
             return BadRequest(new { error = "Missing 'image' file part." });
         }
 
-        byte[] pngBytes;
+        using (await _locks.AcquireAsync(frame.Name, cancellationToken).ConfigureAwait(false))
-        await using (var stream = file.OpenReadStream())
         {
-            pngBytes = _pipeline.Process(stream, frame);
+            byte[] pngBytes;
-        }
+            await using (var stream = file.OpenReadStream())
+            {
+                pngBytes = _pipeline.Process(stream, frame);
+            }
 
-        return await FinishUploadAsync(frame, pngBytes, cancellationToken).ConfigureAwait(false);
+            return await FinishUploadAsync(frame, pngBytes, cancellationToken).ConfigureAwait(false);
+        }
     }
 
     [HttpPost("{name}/image-url")]
@@ -73,23 +80,26 @@ public sealed class FramesController : ControllerBase
             return BadRequest(new { error = "Missing or invalid 'url'." });
         }
 
-        Stream source;
+        using (await _locks.AcquireAsync(frame.Name, cancellationToken).ConfigureAwait(false))
-        try
         {
-            source = await _urlFetcher.FetchAsync(uri, cancellationToken).ConfigureAwait(false);
+            Stream source;
-        }
+            try
-        catch (ImageFetchException ex)
+            {
-        {
+                source = await _urlFetcher.FetchAsync(uri, cancellationToken).ConfigureAwait(false);
-            return StatusCode(StatusCodes.Status502BadGateway, new { error = ex.Message });
+            }
-        }
+            catch (ImageFetchException ex)
+            {
+                return StatusCode(StatusCodes.Status502BadGateway, new { error = ex.Message });
+            }
 
-        byte[] pngBytes;
+            byte[] pngBytes;
-        await using (source)
+            await using (source)
-        {
+            {
-            pngBytes = _pipeline.Process(source, frame);
+                pngBytes = _pipeline.Process(source, frame);
-        }
+            }
 
-        return await FinishUploadAsync(frame, pngBytes, cancellationToken).ConfigureAwait(false);
+            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) =>
 {