The 2026-06-03 handoff localized the failing Core tests to the BSP Path 5
step-up CLIMB (find_walkable/step_sphere_down). An ITestOutputHelper capture
of B1 disproved that: the climb code is correct (matches ACE
Polygon.adjust_sphere_to_plane / BSPTree.step_sphere_down exactly). The real
bug is the A6.P4 near-miss dispatch in FindCollisions' Path 5 (Contact
branch), which diverged from retail three ways:
1. Recorded a near-miss NegPolyHit UNCONDITIONALLY. Retail gates both
set_neg_poly_hit calls behind `if (num_sphere > 1)`
(acclient_2013_pseudo_c.txt:323852).
2. Checked the foot sphere's near-miss before the head's. Retail checks
the head (sphere1) first.
3. Mapped foot->neg_step_up=false / head->true. Retail maps head(index 0)
->false (slide), foot(index 1)->true (step-up), per
SPHEREPATH::set_neg_poly_hit (:323279, neg_step_up = arg2).
For B1's single foot sphere, the spurious near-miss -> outer loop
`!NegStepUp -> SetCollisionNormal + Collided` -> revert: the grounded mover
wedged at x=0.1 and never advanced to the wall to step up. With the verbatim
gate, a single-sphere near-miss records nothing, the sphere advances,
full-hits the wall, and step_sphere_up climbs the 0.25 m step (verified via
probe capture: foot ends at (0.6, 0, 0.25)).
The Holtburg cottage door still blocks faithfully (door slab (0,-1,0) normal,
stops in front of the door) when the scenario has a real floor — confirmed
this change does not regress the door.
The two BSPQueryTests Path5 near-miss tests used a single sphere (the very
non-retail assumption that caused this wedge); converted to the production
2-sphere shape where the head sphere records the near-miss, matching retail.
Core 1312 pass / 4 fail (the 4 pre-existing: 3 door documents-the-bug + D4
airborne, none regressed here); App 177 green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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