The publisher and developer splash logos rendered correctly, but a
fullscreen OPAQUE WHITE diagonal half-triangle flashed at boot, before
each logo, and persisted across the dev-logo transition — canary shows a
black background there. Readback-isolated it (env-gated frontbuffer grid
+ per-draw inventory, both removed) to the background-fill draws.
ROOT (measured, refutes the prior "saturate/interpreter/depth" guesses):
the position-only VS `0xd4c14f46` (one vfetch → oPos; exports NO color)
paired with PS `0xed732b5a` (`ocolor0 = interp0`). The iterate-3T
translator seeded `ointerp[0] = (1,1,1,1)` "so a VS that only exports
position still yields a visible non-zero color" — a debug FAKE: it
injects white that no guest value backs. So that fill's interp0 stayed
white → opaque-white fullscreen triangle. Vertex windows of a WHITE frame
and a steady BLACK frame were byte-identical; served_translated=true for
all of them and depth is disabled in the replay, so the white came purely
from the injected seed, not saturate/interp/depth.
FIX (UI-translator only, golden byte-identical):
- translator.rs: default un-exported interpolators to (0,0,0,0) instead
of seeding interp0 white. A position-only VS now contributes nothing
visible under its real blend (RGB=0 → black; A=0 → premult transparent),
matching canary; every VS that really exports interp0 (the logo
`0x03b7b020`, the color fill `0x36660986`) overwrites the seed → logos
unaffected.
- app.rs: clear the splash frontbuffer to BLACK, not the iterate-3S navy
placeholder `[0.04,0.04,0.06]` (never matched to the guest). The fill is
a fullscreen Xbox-360 RectangleList drawn as a single triangle in the
replay (4th implied corner not yet synthesized), so its uncovered half
exposed the clear; black makes the transition uniformly black like the
oracle. (Full RectangleList→rectangle expansion is a separate follow-up.)
READBACK (env-gated, removed): white-heavy frames 200+ → 0; navy frames
240 → 0; transition frames uniformly black; the publisher logo (white
text + red dots) and the developer logos (colored, on black) still
render. Determinism: changes feed only the UI translator/clear; n50m
--gpu-inline --stable-digest byte-identical 2× and matches the committed
golden (--expect exit 0). cargo test --workspace 686 passed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
c62a355418