fix: prevent QUIC heartbeat stalls and isolate TCP retransmission counters [CI] [SKIP TESTS]

backend/shared/tests/MoShiro.Protocol.Tests/TcpWireTests.cs

@@ -0,0 +1,30 @@
+namespace MoShiro.Protocol.Tests;
+
+public sealed class TcpWireTests
+{
+    [Theory]
+    [InlineData(0)]
+    [InlineData(64)]
+    [InlineData(16384)]
+    public async Task Message_UsesOneWriteForPrefixAndBody_AndPreservesFraming(int size)
+    {
+        using var stream = new CountingStream();
+        byte[] body = Enumerable.Range(0, size).Select(i => (byte)i).ToArray();
+        await TcpWire.WriteMessageAsync(stream, body, default);
+        Assert.Equal(1, stream.Writes);
+        stream.Position = 0;
+        Assert.Equal(body, await TcpWire.ReadMessageAsync(stream, default));
+        Assert.Null(await TcpWire.ReadMessageAsync(stream, default));
+    }
+
+    private sealed class CountingStream : MemoryStream
+    {
+        public int Writes { get; private set; }
+
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            Writes++;
+            return base.WriteAsync(buffer, cancellationToken);
+        }
+    }
+}