Extends the existing [indoor-bsp] probe surface in FindEnvCollisions
with a per-call [indoor-walkable] line gated on
PhysicsDiagnostics.ProbeIndoorBspEnabled (no new flag). Logs the
synthesized contact plane, the polyId hit, and the signed Z gap (dz)
between foot and plane.
Lets the visual-verification step distinguish "FindWalkableSphere
picked the right polygon" from "FindWalkableSphere returned a miss
and we fell through to outdoor-terrain backstop", which is critical
for triaging any remaining indoor collision oddities after the BSP
port lands.
Runtime-toggleable via the existing DebugPanel "Indoor BSP probe"
checkbox; zero cost when disabled.
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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