An upload of a storage image up to 1 MiB reads the surface's guest bytes
into a baseline (#1599), which a later write-back compares against for
blocks the CPU stamped. When a unit shadow, another image's pending
results or a recorded GPU store covers the surface, that read goes
through the flush hook: the shadow is published and the worker waits for
the GPU, although the upload itself runs on the GPU from the import.
The baseline is now taken only when nothing of that kind overlaps the
surface. Otherwise the image has none, and its write-back keeps the CPU's
bytes for stamped blocks, the rule before #1599. TechnicalDebt's entry
names the condition.
agc_storage_baseline_settled creates a storage image over a watched host
import with a recorded store pending over part of it and checks that the
upload did not submit the open batch; without the change the baseline
read syncs on that store. agc_unchanged_cpu_stamps (#1599) still passes.
PPSA14632 (LEGO Horizon Adventures) refreshes such images about 870
times per 10 s from queue 0 dispatches: the hook's recorded-store syncs
go from about 3400 waiting 4.0 s to about 630 waiting 0.3 s per 10 s,
and a direct dispatch's device call from 356 to 107 us.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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