perf(worker): pooled frame buffers — brings the net48 codec up to the gateway side's GWC-30 pattern

src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerFrameReader.cs

@@ -9,11 +9,21 @@ using ZB.MOM.WW.MxGateway.Contracts.Proto;
 namespace ZB.MOM.WW.MxGateway.Worker.Ipc;
 
 /// <summary>Reads length-prefixed WorkerEnvelope protobuf frames from a stream.</summary>
+/// <remarks>
+///     <see cref="ReadAsync"/> is not reentrant: the reader keeps a per-instance length-prefix scratch
+///     buffer, so exactly one consumer may be inside a read at a time. That matches how the reader is
+///     used — a single read loop per <c>WorkerPipeSession</c>, with the startup handshake read
+///     completing before the loop starts.
+/// </remarks>
 public sealed class WorkerFrameReader
 {
     private readonly WorkerFrameProtocolOptions _options;
     private readonly Stream _stream;
 
+    // Reused across frames rather than allocated per read (GWC-30). Safe because ReadAsync is
+    // single-consumer by construction; the prefix is fully overwritten by every read.
+    private readonly byte[] _lengthPrefix = new byte[sizeof(uint)];
+
     /// <summary>Initializes the reader with a stream and protocol options.</summary>
     /// <param name="stream">Stream to read frames from.</param>
     /// <param name="options">Protocol options for frame validation.</param>
@@ -30,10 +40,9 @@ public sealed class WorkerFrameReader
     /// <returns>The validated <see cref="WorkerEnvelope"/> read from the stream.</returns>
     public async Task<WorkerEnvelope> ReadAsync(CancellationToken cancellationToken = default)
     {
-        byte[] lengthPrefix = new byte[sizeof(uint)];
-        await ReadExactlyOrThrowAsync(lengthPrefix, lengthPrefix.Length, cancellationToken).ConfigureAwait(false);
+        await ReadExactlyOrThrowAsync(_lengthPrefix, sizeof(uint), cancellationToken).ConfigureAwait(false);
 
-        uint payloadLength = ReadUInt32LittleEndian(lengthPrefix);
+        uint payloadLength = ReadUInt32LittleEndian(_lengthPrefix);
         if (payloadLength == 0)
         {
             throw new WorkerFrameProtocolException(