Opening a panel or resizing the window while pinned to the end of an idle
session bounced the timeline and left it above the end with the pin
released. Every row re-wraps on a width change and the list's total
content length lags a frame behind the rows, so anything scrolling to the
end from it (the list's own maintainScrollAtEnd, scrollHeight) landed on a
blank tail or short of the real end; the idle branch then released the pin
instead of recovering.
An idle session no longer hands end-keeping to the list at all: the hook's
same-frame pin owns it, and during a width resize it holds the measured
bottom of the last real row plus the list footer, for streaming readers
too. The footer size was missing from that measurement (the list does not
expose it through getState) and left the viewport short by the tail
spacer; it now arrives through onMetricsChange. Size compensation applies
only to a reader who left the end.
The follow re-arm band is half a viewport instead of 40px: leaving the end
is decided by a real gesture only, so the band now only decides how close
a reader must come back before follow re-arms.
Testing: scroll module tests updated (footer in the real end, half-viewport
band with a 40px floor); ui type-check and lint; measured in headless
Chrome that scrollTop equals the maximum on every frame of a panel toggle,
a height change and a combined resize, where the previous build ended 122px
and 462px above the end.
Bohdan Triapitsyn
37f5021715