GHSA-gcx5-hxj7-gpqq

### Impact The streaming decoder reparses an incomplete container from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack value across many small chunks, causing quadratic CPU usage and blocking the event loop. ### Patches The decoder now preserves incremental container state so completed elements are not parsed again when more input arrives. ### Workarounds Buffer each complete MessagePack value before decoding it, or limit the number of chunks accepted for a single value.