diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index 08b8e71..d316c01 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -1944,6 +1944,16 @@ void
 			// (the keyboard-steering skip); pure spin/walk never showed it (one stream).
 			// Save the heading, let DeadReckon own the LINEAR channel, then override
 			// the angular result with the original's incremental integration.
+			// ROOT-MOTION peer POSITION (authentic FUN_004ab1c8: the clip's travel
+			// drives the body between records; pose records re-anchor).  Save the
+			// position so the engine velocity-lerp result can be discarded below
+			// (BT_DR_POS=1 restores the velocity dead-reckon for A/B).
+			// DEFAULT: engine velocity dead-reckon (best-measured: ratio 1.0022).  The
+			// coupled root-motion experiment (BT_ROOT_POS=1) needs the MASTER-side
+			// gait mirror to stop the authority tug-of-war (measured ratio 1.86) --
+			// the completion path is mapped in the session notes.
+			static const int s_drPos = getenv("BT_ROOT_POS") ? 0 : 1;
+			Point3D replPrevPos = localOrigin.linearPosition;
 			Quaternion replPrevHeading = localOrigin.angularPosition;
 			DeadReckon(dt);							// engine reckoner: LINEAR position/velocity
 			if (angSyncLatch)
@@ -1960,6 +1970,8 @@ void
 								   &replPrevHeading, &replAngStep);	// exact FUN_00409f58
 			}
 			localOrigin.angularPosition.Normalize();
+			if (!s_drPos)
+				localOrigin.linearPosition = replPrevPos;	// root-motion mode: gait applies travel below
 			localToWorld = localOrigin;
 
 			// RENDER-vs-SIM decoupling probe: publish the heading the RENDER will
@@ -2122,7 +2134,48 @@ void
 				// once so a direct run-state entry can't slew from -4.3e8.
 				if (legCycleSpeed < -100.0f || legCycleSpeed > 200.0f)
 					legCycleSpeed = 0.0f;
-				(void)AdvanceLegAnimation(dt);		// joints only; travel = DeadReckon
+				const Scalar replLegAdv = AdvanceLegAnimation(dt);	// joints + ROOT TRAVEL
+				// AUTHENTIC coupled position (mirror of the master's world-step at
+				// mech4.cpp:3325-3336 == Mech::IntegrateMotion tail @004ab1c8): between
+				// records the body advances by the CLIP'S OWN travel rotated by the
+				// heading -- feet and ground are locked BY CONSTRUCTION, so cadence-vs-
+				// travel mismatch (the speed-change glitch) is structurally impossible.
+				// A pose record re-anchors onto the authoritative position
+				// (poseSyncLatch, armed by every type-0 read).  adv is SIGNED by the SM
+				// (reverse clips return negative travel; master dir==1.0 in SM mode).
+				if (!s_drPos)
+				{
+					// POSE-SYNC OFFSET DECAY (authentic FUN_004ab1c8 motionEventVector
+					// mechanism): a record does NOT snap the body -- the correction offset
+					// is absorbed over ~1/3s while the clip's root motion keeps driving, so
+					// the feet never pop and the position converges to authority.
+					static Vector3D s_rmErr[2]; // per-instance would be a member; one replicant per node in practice
+					Vector3D &rmErr = s_rmErr[0];
+					if (poseSyncLatch)
+					{
+						rmErr.Subtract(updateOrigin.linearPosition, localOrigin.linearPosition);
+						poseSyncLatch = 0;
+					}
+					{
+						Scalar k = dt * 3.0f; if (k > 1.0f) k = 1.0f;	// ~1/3s absorption
+						localOrigin.linearPosition.x += rmErr.x * k;
+						localOrigin.linearPosition.y += rmErr.y * k;
+						localOrigin.linearPosition.z += rmErr.z * k;
+						rmErr.x -= rmErr.x * k; rmErr.y -= rmErr.y * k; rmErr.z -= rmErr.z * k;
+					}
+					if (replLegAdv != 0.0f)
+					{
+						Vector3D rmLocal(0.0f, 0.0f, -replLegAdv);	// forward = -Z, per-frame DISTANCE
+						Matrix34 rmOrient;
+						Matrix34::FromQuaternion(&rmOrient, &localOrigin.angularPosition);
+						Vector3D rmWorld;
+						FUN_00408744(&rmWorld, (Scalar *)&rmLocal, &rmOrient);
+						localOrigin.linearPosition.x += rmWorld.x;
+						localOrigin.linearPosition.y += rmWorld.y;
+						localOrigin.linearPosition.z += rmWorld.z;
+					}
+					localToWorld = localOrigin;				// refresh with the coupled position
+				}
 
 				// GAIT-EVENNESS probe (BT_GAITEV, 1s stats): the metric of the VISIBLE
 				// speed-change glitch -- per-frame leg-clip advance regularity + leg-state
@@ -3707,6 +3760,10 @@ void
 				// makes the cadence regular + dense (records ~1 frame apart), so the
 				// horizon prediction matches and the lerp tracks smoothly.  On a LAN
 				// this is a handful of small packets/frame -- negligible.
+				// Dense while moving: with the gait-driven peer, the master's velocity
+				// mirror no longer models the peer, so the deadband under-sends and the
+				// peer diverges (measured 11u snaps).  Dense records keep the correction
+				// offset tiny; the peer absorbs it via the authentic pose-sync decay.
 				static const int s_denseTx = getenv("BT_NO_DENSE_TX") ? 0 : 1;
 				const Logical moving = (liveSpdSq > 0.25f);
 				if (