The 0x50 header word, which the first section of this page had dismissed as "a
large value", is two u16 counts: vertices and triangles. They give the two
remaining blocks their stride, and every derived length is exact in 11/11 --
len(0x54) == align16(12*nv), len(0x58) == align16(6*nt), and nt equals the
bounding-sphere count decoded last iteration.
Checks that cannot pass by accident:
* sphere i is the TIGHT bounding sphere of triangle i, 4768/4768, with
max|v-c|/r median 0.99990 (a fixed 1.0001 epsilon), against a 1.32%
random-triangle control;
* the mesh is watertight -- every edge shared by exactly two triangles,
7152/7152, zero degenerate triangles, zero unreferenced vertices;
* the two smallest objects are 8 vertices and 12 triangles whose positions
are the eight +-250000 corners of the map bbox: a bare bounding cube.
The cell lists are a correct broad phase: with an exact triangle/box SAT test
only 3 overlapping triangles in 18 577 entries are absent, so a query walking
one cell's list cannot miss a hit. The 730 conservative extras bracket the
builder's own test between exact-SAT and AABB, which retires the 18 unexplained
"sphere misses" from the previous commit as that same margin.
mcol_probe.py gains `mesh` and `obj`; `verify` now runs all three checks and its
output is recorded in docs/re/data/mcol-verify.txt.
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