OPC # 0001: Extract OPC into standalone repo

ControlPlane.Api/Services/SseEventBus.cs

@@ -0,0 +1,38 @@
+using ControlPlane.Core.Messages;
+using System.Collections.Concurrent;
+using System.Threading.Channels;
+
+namespace ControlPlane.Api.Services;
+
+/// <summary>
+/// Thin in-process pub/sub for SSE. MassTransit consumer writes here;
+/// the SSE endpoint reads and streams to the browser.
+/// </summary>
+public sealed class SseEventBus
+{
+    private readonly ConcurrentDictionary<Guid, List<Channel<ProvisioningProgressEvent>>> _subs = new();
+
+    public void Publish(ProvisioningProgressEvent evt)
+    {
+        if (!_subs.TryGetValue(evt.JobId, out var channels)) return;
+        lock (channels)
+            foreach (var ch in channels)
+                ch.Writer.TryWrite(evt);
+    }
+
+    public Channel<ProvisioningProgressEvent> Subscribe(Guid jobId)
+    {
+        var ch = Channel.CreateUnbounded<ProvisioningProgressEvent>();
+        _subs.GetOrAdd(jobId, _ => []).Add(ch);
+        return ch;
+    }
+
+    public void Unsubscribe(Guid jobId, Channel<ProvisioningProgressEvent> channel)
+    {
+        if (_subs.TryGetValue(jobId, out var channels))
+        {
+            lock (channels) channels.Remove(channel);
+            channel.Writer.TryComplete();
+        }
+    }
+}