Fix chunk drop in incremental reader by buffering pending chunks

ReadIncrementalInstructionBase<T> previously stored each incoming chunk
in a single _latestChunk field. When several ChunkReceived FFI events
were dispatched on the same sync-context flush (routine between Unity
frames), OnChunk overwrote the field before the consumer coroutine
could resume from its yield, silently dropping earlier chunks.

Queue chunks that arrive while a prior read is still pending. Reset()
advances _latestChunk to the next queued chunk and keeps
IsCurrentReadDone true so the next yield completes immediately, draining
the buffer before waiting for more FFI events.

Flips DataStreamIncrementalReadTests from failing to passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: MaxHeimbrock

Runtime/Scripts/DataStream.cs

@@ -77,6 +77,7 @@ internal StreamError(Proto.StreamError proto) : base(proto.Description) { }
     public abstract class ReadIncrementalInstructionBase<TContent> : StreamYieldInstruction
     {
         private readonly ulong _handleValue;
+        private readonly Queue<TContent> _pendingChunks = new();
         private TContent _latestChunk;
 
         /// <summary>
@@ -107,8 +108,26 @@ protected ReadIncrementalInstructionBase(FfiHandle readerHandle)
 
         protected void OnChunk(TContent content)
         {
-            _latestChunk = content;
-            IsCurrentReadDone = true;
+            if (IsCurrentReadDone)
+            {
+                // Consumer hasn't yielded since the last chunk; buffer until Reset().
+                _pendingChunks.Enqueue(content);
+            }
+            else
+            {
+                _latestChunk = content;
+                IsCurrentReadDone = true;
+            }
+        }
+
+        public override void Reset()
+        {
+            base.Reset();
+            if (_pendingChunks.Count > 0)
+            {
+                _latestChunk = _pendingChunks.Dequeue();
+                IsCurrentReadDone = true;
+            }
         }
 
         protected void OnEos(Proto.StreamError protoError)

Tests/EditMode/DataStreamIncrementalReadTests.cs

@@ -1,12 +1,11 @@
 using System;
 using System.Collections.Generic;
-using LiveKit;
 using LiveKit.Internal;
 using NUnit.Framework;
 
 namespace LiveKit.EditModeTests
 {
-    public class DataStreamIncrementalReadTests
+    public class DataStreamTests
     {
         private sealed class TestIncrementalReader : ReadIncrementalInstructionBase<string>
         {