How to extract specific cited document IDs for a custom logging tool?

I'm building an AI Agent in Oracle Fusion Agent Studio with a custom tool (chat_store) to log chat history. I need to pass the actual cited document IDs or names to this logging tool, but the LLM keeps returning null.

The Issue:

• The LLM only generates the search query. The system/middleware injects the searchable documentIds array behind the scenes.
• Asking the LLM to extract the IDs via prompt instructions fails.
• Passing the IDs via an Input Variable logs the entire searchable array, not just the specific documents the agent actually used for its answer.

My Questions:

• Is there a built-in system expression (like ${system.citations}) to automatically capture the metadata of the specific documents used in the RAG response?