diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 75857de..af85140 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -3241,6 +3241,56 @@ public sealed class GameWindow : IDisposable
                 // slerp doesn't visibly rotate from Identity to truth.
                 rmState.Body.Orientation = rot;
             }
+
+            // L.3.1 Task 4: env-var gated retail-faithful MoveOrTeleport routing.
+            // Mirrors CPhysicsObj::MoveOrTeleport (acclient @ 0x00516330).
+            // Enabled only when ACDREAM_INTERP_MANAGER=1 to keep default behavior
+            // identical to before this commit. Legacy hard-snap path remains below.
+            if (System.Environment.GetEnvironmentVariable("ACDREAM_INTERP_MANAGER") == "1")
+            {
+                // CPhysicsObj::MoveOrTeleport router (acclient @ 0x00516330):
+                //   - stale instance/position seq → ignore (TODO: IsStaleSequence not yet plumbed)
+                //   - teleport-seq newer or no-cell → SetPosition (hard-snap)
+                //   - has_contact false → no-op (TODO: HasContact not on wire — default true for L.3.1)
+                //   - has_contact && distance ≤ 96 → InterpolationManager.Enqueue (queue)
+                //   - has_contact && distance > 96 → SetPositionSimple (slide-snap)
+
+                const float MaxPhysicsDistance = 96f;
+                System.Numerics.Vector3 localPlayerPos =
+                    _playerController?.Position ?? System.Numerics.Vector3.Zero;
+                float dist = System.Numerics.Vector3.Distance(worldPos, localPlayerPos);
+
+                // Default-false: teleport flag not plumbed until sequence comparison lands (Task 5+).
+                bool teleportFlag = false;
+                // Default-true: HasContact not on wire yet (CreateObject.ServerPosition gap).
+                // bool hasContact = true; (implicit — only the teleport and distance branches below)
+
+                if (teleportFlag)
+                {
+                    // SetPosition equivalent: hard-snap position + orientation, clear interp queue.
+                    rmState.Body.Position = worldPos;
+                    rmState.Body.Orientation = rot;
+                    rmState.Interp.Clear();
+                }
+                else if (dist > MaxPhysicsDistance)
+                {
+                    // SetPositionSimple equivalent: slide-snap (clear queue, then hard-snap).
+                    rmState.Interp.Clear();
+                    rmState.Body.Position = worldPos;
+                    rmState.Body.Orientation = rot;
+                }
+                else
+                {
+                    // InterpolationManager.Enqueue equivalent: queue for adjust_offset to walk to.
+                    // NOTE: do NOT touch rmState.Body.Position here — adjust_offset (Task 5) owns it.
+                    float headingFromQuat = ExtractYawFromQuaternion(rot);
+                    rmState.Interp.Enqueue(worldPos, headingFromQuat, isMovingTo: false);
+                }
+
+                // Skip the legacy hard-snap path below.
+                return;
+            }
+
             double nowSec = (now - System.DateTime.UnixEpoch).TotalSeconds;
             System.Numerics.Vector3? serverVelocity = update.Velocity;
             if (serverVelocity is null
@@ -5131,6 +5181,20 @@ public sealed class GameWindow : IDisposable
         return new System.Numerics.Quaternion(0f, 0f, z, w);
     }
 
+    /// <summary>
+    /// Inverse of <see cref="YawToAcQuaternion"/>: extracts the local yaw (rotation
+    /// about the Z axis, in radians) from an AC wire quaternion.
+    /// Yaw=0 faces +X (East). Used by the L.3.1 InterpolationManager routing to
+    /// convert server orientation into the heading expected by <c>InterpolationManager.Enqueue</c>.
+    /// Standard formula: atan2( 2(wz + xy), 1 − 2(y² + z²) ).
+    /// </summary>
+    private static float ExtractYawFromQuaternion(System.Numerics.Quaternion q)
+    {
+        return MathF.Atan2(
+            2f * (q.W * q.Z + q.X * q.Y),
+            1f - 2f * (q.Y * q.Y + q.Z * q.Z));
+    }
+
     private void OnCameraModeChanged(bool _modeBool)
     {
         if (_input is null) return;