In the detail view a thumb on the content resized the sheet whenever the
content could not scroll that way, so reading the list moved the sheet. Only
the handle (the drag strip and the title row) starts a resize now; below it
the content scrolls, in every mode.
The sheet's list gets overscroll-behavior: contain (the list only, not the
pane), so a fling that reaches its end stops there instead of scrolling the
page behind the map.
8133f28b6b