TryFindIndoorWalkablePlane (Phase 2 commit eb0f772) used a linear
first-match XY scan of cellPhysics.Resolved with no Z-proximity test.
For any cell with two walkable polys overlapping in XY at different Z
(cellars, 2nd floors, balconies, stairs spanning floors), it returned
whichever polygon came first in dictionary order — typically the upper
floor when descending, causing the player to be reported below the
synthesized plane → ValidateWalkable fails → falling-stuck. Symptoms
reported by user 2026-05-19: cannot descend into cellar; cannot walk
on 2nd floor; "invisible obstacles at certain spots" (suspected
cascade from wrong-Z ContactPlane misrouting the resolver state).
Fix: route through BSPQuery.FindWalkableSphere (added previous commit),
which wraps the existing retail-faithful FindWalkableInternal
(BSPNODE::find_walkable + BSPLEAF::find_walkable port). Adds a
sphereRadius parameter to TryFindIndoorWalkablePlane so the foot
sphere is built with the actual entity radius rather than a guess.
WalkableAllowance is save/restored via try/finally so the slope
threshold used by walkable_hits_sphere doesn't leak back to the
resolver. Method becomes an instance method (was static) to access
this.SpherePath.
Deletes the now-dead PointInPolygonXY helper.
Updates IndoorWalkablePlaneTests.cs: all TryFindIndoorWalkablePlane
test fixtures now include a PhysicsBSPTree leaf node (required by
the new routing path), calls pass sphereRadius, and the PointInPolygonXY
tests are removed (method deleted). Adds TransitionTypesTests.cs with
an integration test covering two-overlapping-floors selection AND
WalkableAllowance preservation.
Closes (pending visual verification): ISSUES #83.
Spec: docs/superpowers/specs/2026-05-19-indoor-walkable-plane-bsp-port-design.md
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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