What it means
This is not implemented. It is published so that a known gap is visible rather than assumed to be covered.
The intended shape is that the GitHub projection reads the intents a milestone realises, and keeps the milestone open on GitHub while any of them is not satisfied.
How it works today
scripts/github-sync projects each milestone from its derived plan status alone and reads no intent. Closed work the evidence contradicts is refused by the intent-realization gate in this repository (intent-realization-held-to-evidence), not by the tracker.
How to see it
grep -c intent scripts/github-sync # 0What it does not cover
It would still be a projection: GitHub would not decide satisfaction, and closing a milestone there would change nothing here.
Why it exists
A tracker that shows a milestone closed while its intent is false repeats the mistake the intent model exists to correct, one projection further out.