When the indoor cell-BSP query returns OK (no wall collision), the player
is standing on a floor poly inside the cell. Previously the code fell
through to outdoor terrain (SampleTerrainWalkable + ValidateWalkable),
which used the OUTDOOR terrain plane — below the indoor floor due to the
+0.02f Z-bump applied for render z-fight prevention. ValidateWalkable
saw the player 0.5m above the outdoor plane → marked them as airborne
→ walkable=False → falling animation, never recovers.
Adds TryFindIndoorWalkablePlane (internal static for testability): scans
the cell's resolved physics polys for a walkable floor poly (normal.Z >=
0.6664, walkable-slope threshold matching retail) under the player's XY,
transforms its plane + vertices to world space via WorldTransform, and
calls ValidateWalkable with the indoor plane. Adds PointInPolygonXY
(ray-casting even-odd rule, ignores Z). Both are wired just after the
BSP OK branch in FindEnvCollisions; outdoor terrain remains a defensive
backstop if no floor poly is found under the player indoors (rare).
Matches retail's CEnvCell::find_env_collisions behavior: no fall-through
to terrain when the cell BSP successfully completes a query.
Evidence: launch-phase2-verify5.log captured 12,141 walkable=False
events during an indoor session where the player never managed to walk
back outdoor through a door — they got stuck against the indoor wall
and the resolver never re-established a walkable contact plane.
Adds 13 unit tests in IndoorWalkablePlaneTests.cs covering:
- player over floor poly (returns true, plane normal up, plane at correct Z)
- player outside poly XY (returns false)
- no walkable polys (returns false)
- empty Resolved dict (returns false)
- cell with world translation (plane + vertices in world space)
- PointInPolygonXY cases (centre, near corner, on boundary, outside, Z ignored)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
