Stretch the whole file at the ends, not one line

`Modifier.horizontalScroll` builds its own overscroll effect per node, so
with a node per row only the line under the finger bent when the file was
dragged past either end and the rest sat still beside it -- the same
complaint as the offsets, one layer out.

There is an overload that takes the effect instead of making one, and it
leaves the rendering to the caller. So the viewer makes one effect, hands
it to every row, and renders it once on a box around the list: the file
bends as the block it scrolls as. This only works now that every row is
the same width -- rows that disagreed about where the end was would
disagree about when to stretch.

**Not seen working.** Measured on the emulator here: over-dragging well
past the end and capturing mid-gesture produces a frame with no stretch in
it at all, and the list's own vertical overscroll does not appear either,
so this VM cannot show the effect for any scrollable. Noted in
~/.claude/MACHINE.md so the next session does not spend the same half hour
on it. What was checked here is everything either side: the scroll still
reaches both ends, the position survives scrolling vertically, and nothing
else moved. The stretch itself wants a look on the phone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

EXPLORER.md

@@ -181,6 +181,15 @@ can carry, so a minified file is a scroll that stops early rather than a
 crash. Reported by Iris on 2026-09-04 as "it seems to affect different rows
 differently", which is precisely what a per-row range looks like.
 
+**The stretch at the ends is one effect too**, shared by every row and
+rendered once on the box around the list -- `horizontalScroll` makes its
+own per node otherwise, so only the line under the finger bent and the
+rest of the file sat still beside it. That is the same complaint one layer
+further out, and it is only fixable now that every row agrees where the
+end is. It cannot be seen from this VM: the emulator's screenshots come
+back with no stretch in them at all, for any scrollable, so this one is
+checked on the phone.
+
 Line numbers are a gutter in each row, right-aligned, with the gutter
 width taken from the digit count of the line count in the same monospace
 style -- so a 9-line file and a 12,000-line file each get exactly the