Android's WebView shrinks the editor page's visual viewport to the part of
the view that is on screen and pans it to reveal the caret while typing.
The editor is an auto-height WebView inside the composer's ScrollView, so
nothing ever resets that pan: scrolled back to the top, the body is still
drawn shifted up by the pan offset and its first lines sit hidden under the
header fields until a scroll to the very bottom clamps it away.
The page now undoes every pan as it happens (scrolling the page top into
view, since window.scrollTo only moves the layout viewport) and reports the
offset as a `viewportShift` message; the composer scrolls its ScrollView by
the same amount so the caret stays visible. Android only; iOS and the other
RichTextEditor hosts keep their behaviour (hosts without the callback still
get the reset).
Reproduced and verified on a Pixel 4 (Android 13, WebView 153): before,
visualViewport.offsetTop stayed at ~18 px at the top of the composer and
cut the first line; after, it stays 0 and the caret still follows typing
above the keyboard.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
lucletoffeandClaude Opus 5.5
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