fix(items): use retail cylinder range for loot windows

Keep external-container visibility tied to the signed surface gap between the player and container physics cylinders, matching gmExternalContainerUI's authored UseRadius range watcher. This prevents a valid ViewContents response from being closed at ACE's natural approach endpoint.

Port Position::cylinder_distance and ACCWeenieObject::ObjectsInRange into Core with conformance coverage for 3-D separation, overlap, mode precedence, and inclusive boundaries.

Release build succeeds and all 5,895 tests pass with five intentional skips.

Co-authored-by: OpenAI Codex <codex@openai.com>

docs/research/2026-07-17-retail-external-container-looting-pseudocode.md

@@ -15,6 +15,11 @@ Named Sept-2013 retail symbols:
 - `gmExternalContainerUI::ListenToElementMessage @ 0x004CBAD0`
 - `gmExternalContainerUI::SetGroundObject @ 0x004CBBD0`
 - `gmExternalContainerUI::CloseCurrentContainer @ 0x004CBCB0`
+- `CPlayerSystem::CalculateObjectRangeChecks @ 0x0055F360`
+- `CPlayerSystem::RegisterObjectRangeHandler @ 0x005602D0`
+- `ACCWeenieObject::ObjectsInRange @ 0x0058C1A0`
+- `CPhysicsObj::get_distance_to_object @ 0x0050F7A0`
+- `Position::cylinder_distance @ 0x005A97F0`
 - `gmExternalContainerUI::PostInit @ 0x004CBDE0`
 - `gmExternalContainerUI::OnVisibilityChanged @ 0x004CBF50`
 - `gmExternalContainerUI::RecvNotice_SetGroundObject @ 0x004CBFD0`
@@ -128,9 +133,19 @@ ExternalPanel.SetGroundObject(containerId):
     if containerId == 0:
         hide panel
     else:
-        register range watch using root UseRadius
+        register range watch(root, root.UseRadius,
+                             useRadii = true, ignoreZDelta = false)
         show panel
 
+CalculateExternalRangeWatch(root, player):
+    // CPlayerSystem routes the authored range registration through
+    // ACCWeenieObject::ObjectsInRange. With useRadii=true, this is the gap
+    // between the two live physics cylinders, not center-to-center distance.
+    distance = Position.cylinder_distance(
+        root.radius, root.height, root.position,
+        player.radius, player.height, player.position)
+    return distance <= root.UseRadius
+
 ExternalPanel.CloseCurrentContainer():
     if currentExternalRoot == 0:
         return