Configuring Copilot chat retention policies

We're looking at implementing a 30-day retain-and-delete policy for Microsoft Copilot chats and have a couple of questions.

Firstly, is the retention period applied to the chat as a whole or to the individual prompts and responses within that chat?

For example, if a user starts a chat on Day 1 and then goes back into the same chat on Day 20 to ask another question, does that new activity effectively keep the whole chat for another 30 days? Or are the original prompts and responses still deleted 30 days after they were created, regardless of later activity in the same conversation?

Secondly, what happens if a Copilot chat is moved into a Copilot Notebook? Does the same retention policy still apply to the chat content, or does moving it to a notebook change how long it is retained?

More generally, if users need to keep Copilot content for longer than 30 days, what is the recommended approach? For example, would moving the chat to a Notebook preserve it beyond the retention period, or would users need to save the content elsewhere, such as a Word document, SharePoint site or another M365 location?

Any guidance would be appreciated.

Thanks