Your agent keeps rebuilding stuff your team already tried and killed

Ran into this a bunch while vibecoding with longer agent runs.

The agent confidently starts building something a teammate already tried months ago and closed the PR on. It has no way to know, because git only keeps what got merged. Every rejected attempt, and the reason it was rejected, just isn't there. So the agent happily walks into the same wall.

The reasoning behind a codebase (why the timeout is 30, why an approach got dropped) lives in closed PRs and reviews nobody reads again. Your agent can't see any of it.

How are you all handling this? Do you paste past decisions into context by hand, keep a decisions doc, or just catch it in review? Genuinely curious what's working, because review-only has not been enough for me.