feat(physics): Cluster A — indoor BSP collision probe

Adds the [indoor-bsp] probe + ProbeIndoorBspEnabled toggle for the
Indoor walking Phase 1 BSP-cluster investigation. Mirrors the existing
[resolve] / [cell-transit] / [indoor-*] pattern: one log line per
BSPQuery.FindCollisions call from FindEnvCollisions' cell branch,
capturing cell id, sphere local-pos, result TransitionState, and the
hit poly's normal + side-type via the LastBspHitPoly side-channel
(already wired for ProbeBuildingEnabled, now also fires for the indoor
flag).

Toggle via ACDREAM_PROBE_INDOOR_BSP=1 env var or DebugPanel checkbox.
Zero-cost when off.

Predecessor for the three fix commits that will close ISSUES.md
#84/#85/#86 after the capture session.

Spec: docs/superpowers/specs/2026-05-19-indoor-walking-phase1-bsp-cluster-design.md
Plan: docs/superpowers/plans/2026-05-19-indoor-walking-phase1-bsp-cluster.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/BSPQuery.cs

@@ -1215,7 +1215,7 @@ public static class BSPQuery
         {
             collisions.SetCollisionNormal(collisionNormal);
             // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-            if (PhysicsDiagnostics.ProbeBuildingEnabled)
+            if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                 PhysicsDiagnostics.LastBspHitPoly = hitPoly;
             return TransitionState.Collided;
         }
@@ -1228,14 +1228,14 @@ public static class BSPQuery
             // the early-out — collisions.SetCollisionNormal isn't called on
             // this path, but the caller's CollisionInfo.CollisionNormalValid
             // check will catch the parent slide site's normal write instead.
-            if (PhysicsDiagnostics.ProbeBuildingEnabled)
+            if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                 PhysicsDiagnostics.LastBspHitPoly = hitPoly;
             return TransitionState.Collided;
         }
 
         collisions.SetCollisionNormal(collisionNormal);
         // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-        if (PhysicsDiagnostics.ProbeBuildingEnabled)
+        if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
             PhysicsDiagnostics.LastBspHitPoly = hitPoly;
 
         var adjusted = validPos.Center - checkPos.Center;
@@ -1551,7 +1551,7 @@ public static class BSPQuery
                 // is the dominant grounded-player path; without this the
                 // probe's [resolve-bldg] line for every grounded BSP hit was
                 // mis-labeled as "n/a (cylinder)".
-                if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                     PhysicsDiagnostics.LastBspHitPoly = hitPoly0;
 
                 var worldNormal = L2W(hitPoly0!.Plane.Normal);
@@ -1585,7 +1585,7 @@ public static class BSPQuery
                     // L.2d slice 1.5 (2026-05-13): same early-record as foot
                     // sphere — head-sphere wall hits also recurse via
                     // StepSphereUp on the grounded path.
-                    if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                    if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                         PhysicsDiagnostics.LastBspHitPoly = hitPoly1;
 
                     var worldNormal = L2W(hitPoly1!.Plane.Normal);
@@ -1669,7 +1669,7 @@ public static class BSPQuery
                     collisions.SetCollisionNormal(worldNormal0);
                     collisions.SetSlidingNormal(worldNormal0);
                     // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                    if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                    if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                         PhysicsDiagnostics.LastBspHitPoly = hitPoly0;
                     return TransitionState.Slid;
                 }
@@ -1679,7 +1679,7 @@ public static class BSPQuery
                 path.SetCollide(worldNormal0);
                 path.WalkableAllowance = PhysicsGlobals.LandingZ;
                 // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                     PhysicsDiagnostics.LastBspHitPoly = hitPoly0;
                 return TransitionState.Adjusted;
             }
@@ -1709,7 +1709,7 @@ public static class BSPQuery
                         collisions.SetCollisionNormal(worldNormal1);
                         collisions.SetSlidingNormal(worldNormal1);
                         // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                        if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                        if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                             PhysicsDiagnostics.LastBspHitPoly = hitPoly1;
                         return TransitionState.Slid;
                     }
@@ -1718,7 +1718,7 @@ public static class BSPQuery
                     path.SetCollide(worldNormal1);
                     path.WalkableAllowance = PhysicsGlobals.LandingZ;
                     // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                    if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                    if (PhysicsDiagnostics.ProbeBuildingEnabled || PhysicsDiagnostics.ProbeIndoorBspEnabled)
                         PhysicsDiagnostics.LastBspHitPoly = hitPoly1;
                     return TransitionState.Adjusted;
                 }

src/AcDream.Core/Physics/PhysicsDiagnostics.cs

@@ -166,4 +166,33 @@ public static class PhysicsDiagnostics
     /// </summary>
     public static bool DumpSteepRoofEnabled { get; set; } =
         Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEEP_ROOF") == "1";
+
+    /// <summary>
+    /// Indoor walking Phase 1 (2026-05-19). When true, emits one
+    /// <c>[indoor-bsp]</c> line per <see cref="BSPQuery.FindCollisions"/>
+    /// call made from <see cref="Transition.FindEnvCollisions"/>'s indoor
+    /// cell-BSP branch. Captures the cell id, sphere local position,
+    /// resulting <see cref="TransitionState"/>, and the hit poly's id,
+    /// local-normal, and side-type — pinpoints why indoor collision
+    /// returns spurious collisions (#84) and helps cross-check the
+    /// outdoor-in approach path (#85).
+    ///
+    /// <para>
+    /// While true, this also un-gates the diagnostic
+    /// <see cref="LastBspHitPoly"/> side-channel inside
+    /// <see cref="BSPQuery"/> — see the OR'd condition at every poly
+    /// write site. Zero-cost when off.
+    /// </para>
+    ///
+    /// <para>
+    /// Initial state from <c>ACDREAM_PROBE_INDOOR_BSP=1</c>.
+    /// Runtime-toggleable via DebugPanel.
+    /// </para>
+    ///
+    /// <para>
+    /// Spec: <c>docs/superpowers/specs/2026-05-19-indoor-walking-phase1-bsp-cluster-design.md</c>.
+    /// </para>
+    /// </summary>
+    public static bool ProbeIndoorBspEnabled { get; set; } =
+        Environment.GetEnvironmentVariable("ACDREAM_PROBE_INDOOR_BSP") == "1";
 }

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -1217,6 +1217,12 @@ public sealed class Transition
                     };
                 }
 
+                // Indoor walking Phase 1 (2026-05-19): clear the LastBspHitPoly
+                // side-channel before the call so a missed write (no collision)
+                // is greppable as "poly=n/a" in the probe line below.
+                if (PhysicsDiagnostics.ProbeIndoorBspEnabled)
+                    PhysicsDiagnostics.LastBspHitPoly = null;
+
                 // Use the full 6-path BSP dispatcher for retail-faithful collision.
                 // Use pre-resolved polygons (vertices+planes computed at cache time).
                 var cellState = BSPQuery.FindCollisions(
@@ -1231,6 +1237,18 @@ public sealed class Transition
                     Quaternion.Identity,
                     engine);        // engine needed for Path 5 step-up
 
+                if (PhysicsDiagnostics.ProbeIndoorBspEnabled)
+                {
+                    var hit = PhysicsDiagnostics.LastBspHitPoly;
+                    string polyDesc = hit is null
+                        ? "poly=n/a"
+                        : System.FormattableString.Invariant(
+                            $"n=({hit.Plane.Normal.X:F3},{hit.Plane.Normal.Y:F3},{hit.Plane.Normal.Z:F3}) sides={hit.SidesType}");
+                    Console.WriteLine(System.FormattableString.Invariant(
+                        $"[indoor-bsp] cell=0x{sp.CheckCellId:X8} wpos=({footCenter.X:F3},{footCenter.Y:F3},{footCenter.Z:F3}) lpos=({localCenter.X:F3},{localCenter.Y:F3},{localCenter.Z:F3}) lprev=({localCurrCenter.X:F3},{localCurrCenter.Y:F3},{localCurrCenter.Z:F3}) r={sphereRadius:F3} result={cellState} ")
+                        + polyDesc);
+                }
+
                 if (cellState != TransitionState.OK)
                 {
                     if (!ObjectInfo.State.HasFlag(ObjectInfoState.Contact))

src/AcDream.UI.Abstractions/Panels/Debug/DebugPanel.cs

@@ -275,6 +275,9 @@ public sealed class DebugPanel : IPanel
         if (r.Checkbox("Indoor: xform (ACDREAM_PROBE_INDOOR_XFORM)",   ref probeIndoorXform))  _vm.ProbeIndoorXform  = probeIndoorXform;
         if (r.Checkbox("Indoor: cull (ACDREAM_PROBE_INDOOR_CULL)",     ref probeIndoorCull))   _vm.ProbeIndoorCull   = probeIndoorCull;
 
+        bool probeIndoorBsp    = _vm.ProbeIndoorBsp;
+        if (r.Checkbox("Indoor: BSP collision (ACDREAM_PROBE_INDOOR_BSP)", ref probeIndoorBsp)) _vm.ProbeIndoorBsp = probeIndoorBsp;
+
         r.Spacing();
 
         // Cycle / toggle actions live on the VM as Action handles; the

src/AcDream.UI.Abstractions/Panels/Debug/DebugVM.cs

@@ -345,6 +345,20 @@ public sealed class DebugVM
         set => RenderingDiagnostics.ProbeIndoorCullEnabled = value;
     }
 
+    /// <summary>
+    /// Indoor walking Phase 1 (2026-05-19). Runtime mirror of
+    /// <c>PhysicsDiagnostics.ProbeIndoorBspEnabled</c> (env var
+    /// <c>ACDREAM_PROBE_INDOOR_BSP</c>). Toggling here flips the
+    /// <c>[indoor-bsp]</c> probe live — no relaunch required.
+    /// Physics-side companion to the five render-side
+    /// <c>ProbeIndoor*</c> mirrors directly above.
+    /// </summary>
+    public bool ProbeIndoorBsp
+    {
+        get => PhysicsDiagnostics.ProbeIndoorBspEnabled;
+        set => PhysicsDiagnostics.ProbeIndoorBspEnabled = value;
+    }
+
     /// <summary>
     /// Runtime mirror of <c>RenderingDiagnostics.IndoorAll</c> — toggles all
     /// five indoor probes together. No dedicated env var; set any individual

tests/AcDream.UI.Abstractions.Tests/Panels/Debug/DebugVMTests.cs

@@ -1,5 +1,6 @@
 using System.Numerics;
 using AcDream.Core.Combat;
+using AcDream.Core.Physics;
 using AcDream.UI.Abstractions.Panels.Debug;
 
 namespace AcDream.UI.Abstractions.Tests.Panels.Debug;
@@ -285,4 +286,26 @@ public sealed class DebugVMTests
         Assert.Equal(1, weatherHits);
         Assert.Equal(1, wireHits);
     }
+
+    [Fact]
+    public void ProbeIndoorBsp_ForwardsToPhysicsDiagnostics()
+    {
+        var originalEnabled = PhysicsDiagnostics.ProbeIndoorBspEnabled;
+        try
+        {
+            var vm = NewVm();
+
+            vm.ProbeIndoorBsp = true;
+            Assert.True(PhysicsDiagnostics.ProbeIndoorBspEnabled);
+            Assert.True(vm.ProbeIndoorBsp);
+
+            vm.ProbeIndoorBsp = false;
+            Assert.False(PhysicsDiagnostics.ProbeIndoorBspEnabled);
+            Assert.False(vm.ProbeIndoorBsp);
+        }
+        finally
+        {
+            PhysicsDiagnostics.ProbeIndoorBspEnabled = originalEnabled;
+        }
+    }
 }