feat(engine): WebhookRouter (TCS + first-write-wins + timeout)

src/VolcanicCore.Api/Engine/WebhookRouter.cs

@@ -0,0 +1,35 @@
+using System.Collections.Concurrent;
+
+namespace VolcanicCore.Api.Engine;
+
+public sealed record WebResponsePayload(int StatusCode, string Body, string ContentType);
+
+public sealed class WebhookRouter
+{
+    private sealed record Entry(
+        TaskCompletionSource<WebResponsePayload?> Tcs,
+        CancellationTokenSource Timeout);
+
+    private readonly ConcurrentDictionary<Guid, Entry> _pending = new();
+
+    public Task<WebResponsePayload?> Register(Guid id, TimeSpan timeout)
+    {
+        var tcs = new TaskCompletionSource<WebResponsePayload?>(TaskCreationOptions.RunContinuationsAsynchronously);
+        var cts = new CancellationTokenSource(timeout);
+        cts.Token.Register(() =>
+        {
+            if (_pending.TryRemove(id, out _))
+                tcs.TrySetResult(null);   // timeout fires as null
+        });
+        _pending[id] = new Entry(tcs, cts);
+        return tcs.Task;
+    }
+
+    // Returns true iff this call was the first to resolve the channel.
+    public bool Resolve(Guid id, WebResponsePayload payload)
+    {
+        if (!_pending.TryRemove(id, out var entry)) return false;
+        entry.Timeout.Dispose();
+        return entry.Tcs.TrySetResult(payload);
+    }
+}

src/VolcanicCore.Api/Program.cs

@@ -117,6 +117,8 @@ builder.Services.AddSingleton<ConnectionInstanceRegistry>();
 builder.Services.AddSingleton<IConnectionInstanceRegistry>(sp =>
     sp.GetRequiredService<ConnectionInstanceRegistry>());
 
+builder.Services.AddSingleton<WebhookRouter>();
+
 var app = builder.Build();
 
 // Apply migrations at boot.