The rows past the fold could not be reached at all: the pane grew to fit its
content instead of scrolling, and the page has overflow hidden, so they were
simply gone.
A grid item defaults to min-height: auto, which means it refuses to shrink
below its content's intrinsic size. The span-tree pane is a grid item, so on a
trace with enough rows it expanded past its track -- measured at 704px inside a
593px row -- and the inner overflow:auto never had a reason to engage.
min-width: 0 was already there; min-height: 0 is the one that mattered, and is
now set on both panes and on every child of the grid.
Verified by measurement rather than by eye, since the symptom is geometry:
before, waterfall.scrollHeight == clientHeight (nothing to scroll) while the
container overflowed. After, the pane fits its track, the inner scroller has
the full 111px of overflow, and scrolling reaches the last row. Checked the
stacked narrow layout too, where the same grid becomes rows.
The trace list was never affected -- its scroll container already had
min-height: 0 -- and still scrolls 120 rows correctly.
Also makes the CDP screenshot helper print the value its injected script
returns, which is what turned this from a guess into a measurement.
zzg
13b7ebfe2f