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Bug description
The MessageChatMemoryAdvisor.before method does not properly handle the case when a user modifies an existing user message that has already received a response from the AI model.
Currently, when a user resends a modified message:
The old user message remains in the chat memory
The corresponding assistant response to that old message also remains in the chat memory
The new user message is simply appended to the memory
This leads to inconsistent chat history where both the old and new versions of a message (and their respective responses) exist in the conversation.

Environment
version： 1.0.0 and main

Steps to reproduce

1. in before method add log for example:chatClientRequest.prompt().getInstructions();
2. send userMessage and modify it;
3. see log old userMessage is exist ;

Expected behavior
When a user sends a message that already exists in the chat history:
The existing user message should be removed from memory
The assistant response to that message should also be removed from memory
The new user message should be added to the memory
A new assistant response should be generated and added to the memory

Minimal Complete Reproducible example
in before method add log for example:chatClientRequest.prompt().getInstructions();
send userMessage and modify it; see log old userMessage is exist ;