From f845b2241a5314ffdf351c554bb7cafa631b696a Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Tue, 19 May 2026 22:02:06 +0200
Subject: [PATCH] feat(physics): add [indoor-walkable] probe line

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>
---
 src/AcDream.Core/Physics/TransitionTypes.cs | 29 ++++++++++++++++++---
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index 50dc718..ae2b3de 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -1383,10 +1383,31 @@ public sealed class Transition
                 // Retail: CEnvCell::find_env_collisions returns from the cell
                 // branch with the cell's walkable plane set — no fall-through
                 // to terrain.
-                if (TryFindIndoorWalkablePlane(cellPhysics, localCenter, sphereRadius,
-                        out var indoorPlane,
-                        out var indoorVertices,
-                        out uint _))
+                bool walkableHit = TryFindIndoorWalkablePlane(
+                    cellPhysics, localCenter, sphereRadius,
+                    out var indoorPlane,
+                    out var indoorVertices,
+                    out uint hitPolyId);
+
+                if (PhysicsDiagnostics.ProbeIndoorBspEnabled)
+                {
+                    if (walkableHit)
+                    {
+                        // dz = signed gap between foot and synthesized plane.
+                        // Plane: N·p + D = 0  ⇒  pZ_on_plane = -D/N.z (for upward-facing planes)
+                        // gap   = foot.Z - pZ_on_plane = foot.Z - (-D/N.z) = foot.Z + D/N.z
+                        float dz = footCenter.Z + indoorPlane.D / indoorPlane.Normal.Z;
+                        Console.WriteLine(System.FormattableString.Invariant(
+                            $"[indoor-walkable] cell=0x{sp.CheckCellId:X8} wpos=({footCenter.X:F3},{footCenter.Y:F3},{footCenter.Z:F3}) probe={INDOOR_WALKABLE_PROBE_DISTANCE:F2} result=HIT poly=0x{hitPolyId:X4} wn=({indoorPlane.Normal.X:F3},{indoorPlane.Normal.Y:F3},{indoorPlane.Normal.Z:F3}) wD={indoorPlane.D:F3} dz={dz:+0.00;-0.00;+0.00}"));
+                    }
+                    else
+                    {
+                        Console.WriteLine(System.FormattableString.Invariant(
+                            $"[indoor-walkable] cell=0x{sp.CheckCellId:X8} wpos=({footCenter.X:F3},{footCenter.Y:F3},{footCenter.Z:F3}) probe={INDOOR_WALKABLE_PROBE_DISTANCE:F2} result=MISS"));
+                    }
+                }
+
+                if (walkableHit)
                 {
                     return ValidateWalkable(
                         footCenter,