[BUG] Mastra with ai-sdk v5 may cause duplicate assistant messages
# [BUG] Mastra with ai-sdk v5 may cause duplicate assistant messages
Duplicate assistant messages with ai-sdk v5 could not be reproduced in the latest beta, so the issue was closed there. If you hit this, upgrade to the latest beta and retest.
## Context from the issue
gh:mastra-ai/mastra#9370: Issue mastra-ai/mastra#9370 (closed, 32 comments): ### Describe the Bug When using `useChat` from `@ai-sdk/react` to call Mastra's API, assistant messages may have duplicate parts. In the messages list, some assistant messages contain previous parts. It occurred in my project and can also be reproduced 100% in the [Official AI SDK v5 example](https://github.com/mastra-ai/mastra/tree/main/examples/ai-sdk-v5) when sending user messages quickly. It reproduces less frequently at normal chat speed. After some debugging, I found that it might be caused in the call stack `addOne() -> addPartsToLatestMessage() -> pushNewMessagePart()` in [message-listMaintainer review
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