bug fix: system promot repeats in multiple rounds of conversations

[skyduy]

Reproduce the BUG

1. Set breakpoint at

   fast-agent/src/mcp_agent/llm/providers/augmented_llm_openai.py

   Line 163 in 7207208

   executor_result = await self.executor.execute(

2. Starting a multi-round interactive dialog task by

uv run fast-agent setup                # create an example agent and config files
uv run agent.py                        # run your first agent

3. The bug is reproduced as follows:
   

I've fixed the bug where the system prompts for duplicates when creating and running interactive dialogs, but I'm not sure if this affects the use of SimpleMemory under complex projects. Please take the trouble to check!

[evalstate]

Thanks for this - well spotted and very very pleased to get this PR. slightly different fix implemented in the end!