feat(streaming): enforce typed completion queues

Replace the flat deferred list, priority scan, unload bypass, and count-only execution cap with exact destination/control/unload/Near/Far FIFOs behind one typed frame meter. Price worker results before adoption, retain exact retry identity, reject stale generations without payload retention, and publish queue pressure through lifecycle diagnostics.

Tests: dotnet build AcDream.slnx -c Release --no-restore; dotnet test AcDream.slnx -c Release --no-restore (8138 passed, 5 skipped)

tests/AcDream.Core.Tests/Streaming/LandblockStreamerTests.cs

@@ -263,6 +263,34 @@ public class LandblockStreamerTests
         Assert.Equal(43ul, unloaded.Generation);
     }
 
+    [Fact]
+    public async Task CompletionSourcePeekPreservesExactResultAndBacklog()
+    {
+        using var streamer = new LandblockStreamer(loadLandblock: _ => null);
+        streamer.Start();
+        streamer.EnqueueUnload(0xABCE0000u, generation: 44);
+
+        for (int i = 0;
+            i < SpinMaxIterations && streamer.BacklogCount == 0;
+            i++)
+        {
+            await Task.Delay(SpinStepMs);
+        }
+
+        Assert.Equal(1, streamer.BacklogCount);
+        Assert.True(streamer.TryPeek(out LandblockStreamResult? firstPeek));
+        Assert.NotNull(firstPeek);
+        Assert.Equal(1, streamer.BacklogCount);
+        Assert.True(streamer.TryPeek(out LandblockStreamResult? secondPeek));
+        Assert.Same(firstPeek, secondPeek);
+        Assert.Equal(1, streamer.BacklogCount);
+
+        Assert.True(streamer.TryRead(out LandblockStreamResult? consumed));
+        Assert.Same(firstPeek, consumed);
+        Assert.Equal(0, streamer.BacklogCount);
+        Assert.False(streamer.TryRead(out _));
+    }
+
     [Fact]
     public async Task Load_ExecutesLoaderOnWorkerThread()
     {