You prompt the LLM to point out that the clue will be added as is to the conversation, but for the LLM to include a marker instead of the actual text to ensure

You prompt the LLM to point out that the clue will be added as is to the conversation, but for the LLM to include a marker instead of the actual text to ensure that actual critical details are included unchanged. EDIT: Also, having the LLM botch a clue occasionally could be a feature. E.g. a bumbling character that you might need to "interrogate" a bit before you actually get the clue in a way that makes sense, and can't be sure it's entirely correct. That could make some characters more realistic.