Two grounding selection rules failed against live ACE restores before the
right one: (1) first-hit SampleFloorZ returned 0x171's 99.475 ceiling TOP face
over its 94.0 floor (issue111-verify2.log) - the player committed onto the
roof level, and the session's heartbeats poisoned ACE's save with z=99.475;
(2) nearest-to-reference self-confirmed that poison (the reference SAT on the
ceiling face, issue111-verify3.log). Root insight: ceiling/roof top faces are
upward-facing and XY-projectable - geometrically indistinguishable from
floors in the render-ish CellSurface soup. The PHYSICS walkable set (plane
normal.Z >= PhysicsGlobals.FloorZ over the claim's Resolved cell-local
polygons - retail BSPTREE::find_walkable's filter) contains only real floors:
PhysicsEngine.WalkableFloorZNearest transforms into the cell frame, drops on
each walkable plane under the XY, picks nearest the reference.
Verified live (issue111-verify4.log): ACE restored the roof-poisoned
(0xA9B40171, z=99.475); the snap validated the claim and grounded to
z=94.000 - the first fully clean indoor login of the arc:
[snap] claim=0xA9B40171 VALIDATED -> grounded to its walkable floor z=94.000
[cell-transit] 0x00000000 -> 0xA9B40171 pos=(155.525,12.416,94.000)
Baseline: Core 1381 + 4 pre-existing #99 failures + 1 skip; App/UI/Net green.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Projects an XY point onto a cell's floor polygons via brute-force
triangle iteration + barycentric Z interpolation. Fan-triangulates
quads and larger polygons. Returns null when outside all floor
surfaces. Accepts pre-transformed world-space vertex positions so
the caller handles EnvCell coordinate transforms.
Second component of the physics collision engine.
4 new tests, all green.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
