> Design docs from Google Docs to checked-in markdown?

This worked pretty well for the team I'm in. Design docs in Google Docs were really hard to keep in sync with decisions and not properly agent accessible. Initially, we were concerned lack of comments would be an issue, but this didn't really came true - a Slack channel does a good enough job. With this flow, the design author makes a decision and review results, agent propagates it to individual areas, and from those to tasks (those are in MD too), and then copies descriptions to Jira. No more "we changed a thing but missed one place that depends on it", or at least not as bad as before.

Would you mind elaborating on

  from those to tasks (those are in MD too)

We're doing the design docs in MD thing, but are you saying you've gone a step further and have the backlog represented in git too?