Reserve the next sequential static checkpoint using its protocol size and
existing retained-expansion accounting instead of 80% of the parent budget.
Preserve total/live heap protections and explain parent admission failures
with effective capacity, retention estimates and usable retained facts.
Fixes#1911
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>
Co-authored-by: Kaoru0822 <208281322+kaoru0822-kitauji@users.noreply.github.com>
Ysopwnable