From ff548b962c93c255cb79e3e0aa7c34e42530ef97 Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Tue, 19 May 2026 21:22:40 +0200
Subject: [PATCH] refactor(physics): expose hitPolyId from FindWalkableInternal
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Adds a ref ushort hitPolyId parameter to FindWalkableInternal so callers
can identify which polygon was hit. The leaf branch already iterates
foreach (ushort polyId in node.Polygons); this surfaces it.

No behavior change. Existing callers (StepSphereDown, Path 4 Collide)
pass a discard local. The new BSPQuery.FindWalkableSphere wrapper
(next commit) will consume it.

Prep for indoor walkable-plane BSP port — see spec
docs/superpowers/specs/2026-05-19-indoor-walkable-plane-bsp-port-design.md
---
 src/AcDream.Core/Physics/BSPQuery.cs | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/AcDream.Core/Physics/BSPQuery.cs b/src/AcDream.Core/Physics/BSPQuery.cs
index 55dc792..c58594e 100644
--- a/src/AcDream.Core/Physics/BSPQuery.cs
+++ b/src/AcDream.Core/Physics/BSPQuery.cs
@@ -652,6 +652,7 @@ public static class BSPQuery
         Vector3                             movement,
         Vector3                             up,
         ref ResolvedPolygon?                hitPoly,
+        ref ushort                          hitPolyId,
         ref bool                            changed)
     {
         if (node is null) return;
@@ -673,6 +674,7 @@ public static class BSPQuery
                 {
                     changed = true;
                     hitPoly = poly;
+                    hitPolyId = polyId;
                 }
             }
             return;
@@ -686,22 +688,22 @@ public static class BSPQuery
         if (dist >= reach)
         {
             FindWalkableInternal(node.PosNode, resolved, path, validPos, movement, up,
-                                  ref hitPoly, ref changed);
+                                  ref hitPoly, ref hitPolyId, ref changed);
             return;
         }
 
         if (dist <= -reach)
         {
             FindWalkableInternal(node.NegNode, resolved, path, validPos, movement, up,
-                                  ref hitPoly, ref changed);
+                                  ref hitPoly, ref hitPolyId, ref changed);
             return;
         }
 
         // Straddles.
         FindWalkableInternal(node.PosNode, resolved, path, validPos, movement, up,
-                              ref hitPoly, ref changed);
+                              ref hitPoly, ref hitPolyId, ref changed);
         FindWalkableInternal(node.NegNode, resolved, path, validPos, movement, up,
-                              ref hitPoly, ref changed);
+                              ref hitPoly, ref hitPolyId, ref changed);
     }
 
     // -------------------------------------------------------------------------
@@ -1103,9 +1105,10 @@ public static class BSPQuery
         var validPos = new CollisionSphere(checkPos);
         bool changed = false;
         ResolvedPolygon? polyHit = null;
+        ushort _polyId = 0;   // step-down doesn't need the id, but the signature requires it
 
         FindWalkableInternal(root, resolved, path, validPos, movement, up,
-                              ref polyHit, ref changed);
+                              ref polyHit, ref _polyId, ref changed);
 
         if (changed && polyHit is not null)
         {
@@ -1487,10 +1490,11 @@ public static class BSPQuery
         {
             var validPos = new CollisionSphere(sphere0);
             ResolvedPolygon? hitPoly = null;
+            ushort _hitPolyId = 0;   // Path 4 doesn't need the id
             bool changed = false;
 
             FindWalkableInternal(root, resolved, path, validPos, movement, localSpaceZ,
-                                  ref hitPoly, ref changed);
+                                  ref hitPoly, ref _hitPolyId, ref changed);
 
             if (changed && hitPoly is not null)
             {