draft-changelog-entry

Drafts one changelog fragment file under changelog.d/<row-id>.md from PR/commit metadata. Use when: preparing a PR for ship, writing a CHANGELOG entry for a merged or about-to-merge change, or filling changelog.d/ from an initiative in a backlog-sweep state.json. Takes initiative id + commit SHA (or branch name) + backlog row id(s) closed. Non-destructive — emits the fragment file contents for review, never…