The geometry side cache was an 8192-entry HASHED table with no ambiguity check.
Unrelated screen positions shared a slot, so a vertex could be handed a
different vertex's sub-pixel fraction, and eviction changed which triangles got
corrected from frame to frame — moving seams across every mesh.
Both references index this table exactly, one slot per reachable SXY
(beetle-psx vertexCache[0x800*2][0x800*2]; DuckStation 2048x2048), and gate it
on an ambiguity flag so a pixel that two DIFFERENT projections rounded to is
never used. Do the same: direct index, first writer wins, flag on a conflicting
value, allocate lazily on enable so the faithful default costs nothing, and
fail closed to the faithful path if the allocation fails.
Adds a lookup census (attempted / hit / miss_unrecorded / miss_ambiguous) on
geom_correction. With an exact table a miss_unrecorded is a genuine tracking
coverage gap rather than a cache artifact, which is what distinguishes 'the
cache was lossy' from 'the vertex path never reaches us in a matchable form'.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Matthew Stanley
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