Keep a lightweight decision log for a project or a person: one dated line per decision with the choice, the reason, the alternatives, who decided, and a revisit trigger, in a single Markdown file that is grepped rather than browsed, so that why did we do that has an answer six months later. Lighter than an ADR; use for product, process, and scope decisions that do not warrant one. Use when a decision is made in chat or a meeting, when the same debate keeps recurring, or when onboarding someone into a project's history.
