ConvAgent: fix agent voice truncation on remote clients (Opus)

Long ElevenLabs audio messages were cut off on remote clients:
- the client Opus decode buffer was only 32000 bytes (~0.88s), so the
  engine decoder aborted with "Decompression buffer too small" and
  dropped the tail of any packet longer than that;
- the server also encoded a whole message as a single Opus packet, which
  the engine encoder caps at 76 frames (~1.52s), silently dropping the rest.
The host/authority plays raw PCM and never decodes, so standalone and
listen-server hosts were unaffected, which masked the bug.

Fix (HandleAudioReceived + MulticastReceiveAgentAudio_Implementation):
- sub-chunk the Opus encode into <=40-frame (25600-byte, 0.8s) blocks,
  one RPC each: stays under both the 76-frame encode cap and the client
  decode buffer, and keeps each Unreliable RPC small;
- raise the client decode buffer 32000 -> 64*1024 as headroom.

Empirically confirmed: networked client logged 16x "Decompression buffer
too small" with Opus active; standalone (Opus equally active) logged zero.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Unreal/PS_AI_Agent/Plugins/PS_AI_ConvAgent/Source/PS_AI_ConvAgent/Private/PS_AI_ConvAgent_ElevenLabsComponent.cpp

@@ -1231,27 +1231,49 @@ void UPS_AI_ConvAgent_ElevenLabsComponent::HandleAudioReceived(const TArray<uint
 
 		if (OpusEncoder.IsValid())
 		{
-			// Opus path: compress then send.
+			// Opus path: compress then send, in sub-blocks.
-			uint32 CompressedSize = static_cast<uint32>(OpusWorkBuffer.Num());
+			//
-			OpusEncoder->Encode(PCMData.GetData(), PCMData.Num(),
+			// A whole ElevenLabs message can be several seconds. Two hard limits
-				OpusWorkBuffer.GetData(), CompressedSize);
+			// force us to split it before each Encode()/RPC:
+			//   1. UE's Opus encoder caps ONE packet at 76 frames (~1.52s) — frames
+			//      beyond that are silently dropped at encode (VoiceCodecOpus.cpp).
+			//   2. The client decode buffer only holds ~44 frames (~0.88s) before
+			//      the engine decoder aborts with "Decompression buffer too small"
+			//      and drops the packet tail (MulticastReceiveAgentAudio_Implementation).
+			// 40 frames (25600 bytes, 0.8s) stays safely under BOTH, so nothing is
+			// truncated on server or client. It also keeps each Unreliable RPC small.
+			static constexpr int32 BytesPerFrame =
+				(PS_AI_ConvAgent_Audio_ElevenLabs::SampleRate / 50)
+				* PS_AI_ConvAgent_Audio_ElevenLabs::Channels
+				* static_cast<int32>(sizeof(int16));            // 640 at 16kHz mono
+			static constexpr int32 MaxOpusChunkBytes = 40 * BytesPerFrame; // 25600 = 0.8s
 
-			if (CompressedSize > 0)
+			int32 Offset = 0;
+			while (Offset < PCMData.Num())
 			{
-				TArray<uint8> CompressedData;
+				const int32 BlockBytes = FMath::Min(MaxOpusChunkBytes, PCMData.Num() - Offset);
-				CompressedData.Append(OpusWorkBuffer.GetData(), CompressedSize);
 
-				if (bNetAudioDebug)
+				uint32 CompressedSize = static_cast<uint32>(OpusWorkBuffer.Num());
+				OpusEncoder->Encode(PCMData.GetData() + Offset, BlockBytes,
+					OpusWorkBuffer.GetData(), CompressedSize);
+
+				if (CompressedSize > 0)
 				{
-					const float Ratio = (CompressedSize > 0)
+					TArray<uint8> CompressedData;
-						? static_cast<float>(PCMData.Num()) / static_cast<float>(CompressedSize)
+					CompressedData.Append(OpusWorkBuffer.GetData(), CompressedSize);
-						: 0.0f;
+
-					UE_LOG(LogPS_AI_ConvAgent_ElevenLabs, Log,
+					if (bNetAudioDebug)
-						TEXT("[NET-SRV] Opus audio chunk: %u bytes sent (raw %d → %.1fx compression)."),
+					{
-						CompressedSize, PCMData.Num(), Ratio);
+						const float Ratio = static_cast<float>(BlockBytes) / static_cast<float>(CompressedSize);
+						UE_LOG(LogPS_AI_ConvAgent_ElevenLabs, Log,
+							TEXT("[NET-SRV] Opus audio chunk: %u bytes sent (raw %d → %.1fx compression)."),
+							CompressedSize, BlockBytes, Ratio);
+					}
+
+					MulticastReceiveAgentAudio(CompressedData);
 				}
 
-				MulticastReceiveAgentAudio(CompressedData);
+				Offset += BlockBytes;
 			}
 		}
 		else
@@ -2533,7 +2555,12 @@ void UPS_AI_ConvAgent_ElevenLabsComponent::MulticastReceiveAgentAudio_Implementa
 	if (OpusDecoder.IsValid())
 	{
 		// Opus path: decode compressed audio.
-		const uint32 MaxDecompressedSize = 16000 * 2;
+		// Buffer must hold a full packet's decoded PCM. The engine decoder aborts
+		// with "Decompression buffer too small to decode voice" (dropping the
+		// packet tail) if this is smaller than the packet needs. The server caps
+		// packets at 40 frames (25600 bytes); 64KB gives ample headroom even up to
+		// the engine's 76-frame (~48640 bytes) maximum, so no packet is truncated.
+		const uint32 MaxDecompressedSize = 64 * 1024;
 		PCMBuffer.SetNumUninitialized(MaxDecompressedSize);
 		uint32 DecompressedSize = MaxDecompressedSize;
 		OpusDecoder->Decode(AudioData.GetData(), AudioData.Num(),