The indoor branch of FindEnvCollisions called Transition.TryFindIndoorWalkablePlane
every frame to re-synthesize the ContactPlane after BSP returned OK.
The synthesis routed through BSPQuery.FindWalkableSphere ->
walkable_hits_sphere, which correctly rejects tangent contact via
|dist| > radius - epsilon. For a grounded player standing on or
brushing a floor, the foot sphere is tangent: 99.87% MISS rate per
the 2026-05-20 [cp-write] probe (3150 MISS / 3154 calls). Each MISS
fell through to outdoor terrain backstop, writing a ContactPlane
that's below the indoor floor by ~0.02m (the render Z-bump),
marking the player airborne and triggering the falling-animation
stuck symptom user-reported on 2nd-floor walks.
Fix: delete the synthesis + outdoor-fallthrough from the indoor OK
path. ContactPlane is retained from the prior tick's seed
(PhysicsEngine.ResolveWithTransition:583, init_contact_plane
equivalent) or refreshed by BSP Path 3 (step_sphere_down) / Path 4
(land-on-surface) during the same tick. Matches retail's
BSPTREE::find_collisions OK path (acclient_2013_pseudo_c.txt:323938).
Also deletes:
- Transition.TryFindIndoorWalkablePlane (~104 lines incl. doc-comment)
- INDOOR_WALKABLE_PROBE_DISTANCE constant
- [indoor-walkable] probe log line
- IndoorWalkablePlaneTests.cs (8 tests, the helper's coverage)
- TransitionTypesTests.cs (1 test, also tested the helper)
Net: -491 lines. BSPQuery.FindWalkableSphere + its 5 unit tests
retained as the underlying retail-faithful walkable-finder API
(reachable for spawn-placement / teleport-verification / future
debug needs; its doc-comment is updated to reflect the change).
Closes Bug A in the indoor ContactPlane retention phase.
Spec: docs/superpowers/specs/2026-05-20-indoor-walkable-synthesis-removal-design.md.
Plan: docs/superpowers/plans/2026-05-20-indoor-walkable-synthesis-removal.md.
Predecessor: de8ffde (Bug B, BSP world-origin fix).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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