From `expanded` a standard side sheet sits in the layout beside the
content, and the view took it out of the layout the moment it closed:
`data-md-drawer-collapsed` (`display: none` on the root) followed `! open`
at once, so its fade was never seen and the content beside it took the
sheet's width, and the gap, in one jump — in every engine. M3's side
sheets: opening a standard sheet shrinks the body beside it, and closing
gives the room back.
drawer.css: the standard root is a clipping flex box whose `inline-size`
springs between none and the sheet's width, with a negative margin as
wide as its flex parent's gap (`--md-drawer-gap`), on the sheet's own
exit and entry timings; the sheet keeps its width at the root's far edge,
so it is uncovered from its inner edge while it fades. drawer.blade.php:
`settle()`, from `x-effect`, measures the gap on each change and holds
the collapse (`closing`) for the root's and the sheet's closing
durations, read a frame on; reopening lets a pending end go by. The
binding reads `collapsed`, which only `settle()` and the window's width
write: a binding reading `open` ran before `settle()` in the same flush
and, already queued, did not run again once `closing` changed.
ContainmentTest closes the showcase's sheet at 1000px and samples, in the
page, for the root part-way to none while the column beside it has grown
part of the way, then checks the collapse, the column at the row's full
width, and a reopen part-way through the exit ending fully open; it fails
on the previous code in Chrome, Firefox and Safari. OverlayTest pins the
root's declarations and the view's bindings.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
