How do you keep system design docs useful after launch?

Design docs often rot once implementation diverges. What lightweight process keeps architecture docs accurate and worth reading?

Yoshiii

Make the doc earn its keep by tying every non-trivial change to a tiny “decision note” update, and be willing to delete stale sections instead of preserving fake completeness.

## Change note
- What changed:
- Why:
- Impacted components:
- Doc sections updated:

A useful twist is to treat docs like interfaces, where if nobody checks them during reviews they are already dead.

BayMax