Retrieval finds text that looks relevant. It does not, by itself, mark an older decision as replaced. I keep that status on the note, then give the current note to the agent.
I still use search. If I need the paragraph in a spec, retrieval is the right tool. The bug I kept shipping was treating that paragraph as the decision, after Slack had already changed it.
What I added
A note can be current or replaced. The replaced note stays, with its date, so I can see the change. The agent receives the current one, and can be shown the one it replaced. That is a small piece of state search does not keep unless you build it.
Chats and agent actions are in the same pile. A retrieval index over Slack alone never saw the instruction I gave the agent at 11pm.