Records the decision that §5.5.4 recommended and the V5 bring-up now makes
actionable: option (C). No further GL-side attempt is made to re-land V4c or V4d
until the same ported world path has been measured on Vulkan.
The grounds are the three investigation sections read together. A blank run
rasterizes its first world frame correctly - frame 43's occlusion counters,
1,692,830 terrain and 317,561 entity samples, byte-match the parent build - and
then one irreversible event kills every GPU→CPU return channel at once:
readbacks come back RGBA(0,0,0,0) over UI pixels the desktop witness shows on
screen, a guarded glGetQueryObject deadlocks the render thread inside the
driver, and a GPU-timeline query-buffer write never lands on its sentinel.
Present and fences keep running at 5.5 ms throughout, on NO_ERROR from
glGetError and a clean glGetGraphicsResetStatus across 1,814 samples. Five
mechanisms are falsified and four independent instrument faults have turned up,
all of them below the API, all on one driver on one GPU.
That is not a shape any further GL-side bisect is well placed to resolve, so the
document now states the decision rule rather than leaving option (C) as a
recommendation. If the identical RHI world path renders correctly on Vulkan on
this GPU, the driver defect is proven and option (B) is adopted deliberately:
GL keeps the legacy world path through V10 as a documented, scoped exception to
§3.1's no-fork rule, confined to the thin submission seam. If it fails on Vulkan
too, the trigger is in code we own and the hunt resumes against a much smaller
haystack.
Two knock-on edits keep the plan self-consistent rather than leaving the reorder
stated in one place and contradicted in another. The slice table marks V4c and
V4d parked, V4t and V4e-V4h re-sequenced pending the verdict, and V5 shipped.
§5.4's sequencing invariants no longer claim V0→V4h is strictly sequential, and
they now carry the consequence that matters: V6 arrives before V4g and V4h, so
the Vulkan backend honours the contract's literal null target while GL still
carries the transitional inheritance. That makes §5.4's two removal obligations
more binding, not less, and V7's differential must not run until the removal has
happened - otherwise it would surface the divergence as a viewport rendering to
the wrong surface, which post-decision is indistinguishable from the fork option
(B) permits.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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