ATTRIBUTION: thanks to Martin Cleaver https://github.com/mrjcleaver and the Agentics-Foundation https://agentics.org/ -- I took chat notes, and restructured for future reference below.
A lightweight, durable way to capture why an architectural decision was made (not just what was built), so teams can revisit decisions with context instead of re-litigating from scratch.
Tip
ADR = one decision, one file. Keep it durable, searchable, and easy to supersede.