Basic Org-mode operations: headline structure editing and lightweight export.
This is a pragmatic subset of Org (https://orgmode.org/), not a complete implementation. The structural helpers operate on the whole buffer text plus a 0-based cursor line and return the rewritten text (and, where the cursor should follow a moved subtree, its new line). The exporters turn Org markup into Markdown or a small standalone HTML document.
All functions are pure so they can be unit-tested without a live editor.