Ask it like a person
Type /ask which vendor did we pick? in the group, or just ask the bot the question privately. It searches the group's whole history and answers in a sentence or two.
Searching for a word isn't enough, because the answer often doesn't contain it: the message with vendor in it is the question, and the answer — we went with Bravo — came four lines later. So it reads the messages around every match before it answers.
Decisions, kept for you
Each night the bot notes what the group actually settled — not every idea, just the decisions — and /decisions lists them. Nobody has to maintain it.
Privacy
Members who send /optout are left out of search results and answers, not just summaries. Message history is kept for 90 days by default, and the group owner can change that or download the whole archive at any time.
The honest limit
It can only search what it has seen: messages sent after the bot joined the group.