Three compromises were taken deliberately over the last few days and none of
them was written anywhere a future reader would look. So `docs/technical-debt.md`,
and two corrections to the architecture document that the Android change made
untrue the moment it landed.
**TD-1, the Android readback.** §12/6.1 says GPU results never round-trip
through the CPU, and the develop view on Android now does exactly that. That
is worth recording as a breach with reasons rather than quietly leaving a
constraint the code no longer honours — the next person to read §6.1 and then
`DevelopSession::render` would otherwise conclude one of them is a mistake.
The entry carries the device measurements that forced it, why setting
`preTransform` is not a fix available to us, and the three separate things any
one of which would remove it.
**TD-2 and TD-3**, the serial thumbnail fetch and the unbounded drain, were
found while chasing the tearing and are still outstanding. Both have a known
shape for the fix; neither is a bug, and neither should be discovered again
from scratch.
The architecture document said the app renders "through wgpu to Vulkan on both
Linux and Android", which stopped being true at 6267802, and §12/6.1 claimed a
constraint with no exceptions. Both now say what the code does and point at
the debt entry for why.
The numbers are labelled with what they are. TD-1's readback cost has *not*
been measured on the device and says so, and TD-3's figures are from a debug
build and say so — a documented measurement that quietly turns out to be the
wrong build is worse than no measurement.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5
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