fix(anim): Phase L.1c clamp approach velocity to prevent overshoot

User-observed residual after f794832: creature stops to attack but
still runs slightly through the player before stopping.

Cause: at 4 m/s body velocity (RunAnimSpeed × ~1.0 speedMod) and a
60 fps tick (~16 ms), the body advances ~6.4 cm per tick. When dist
falls just below the 0.6 m DistanceToObject arrival threshold, the
arrival predicate fires and zeroes velocity — but the body has
already advanced one full tick INTO the threshold zone. That last
tick is the "running through" the user sees, especially when
combined with a player visual radius of ~0.5 m.

Fix: cap horizontal velocity in the steering branch so the body lands
EXACTLY at the arrival threshold instead of overshooting it. Pure
function in RemoteMoveToDriver (ClampApproachVelocity) so it's
testable; called from GameWindow.cs after apply_current_movement
sets RunForward velocity from the active cycle.

The clamp is a strict scale-down of the X/Y components; Z is left
to gravity / terrain handling. No-op for the flee branch — fleeing
has no overshoot risk by definition.

Tests: 1416 → 1420. Four new clamp scenarios: exact-landing (FP
tolerance), would-overshoot scale-down, already-at-threshold zeroing,
flee no-op.

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -5226,6 +5226,23 @@ public sealed class GameWindow : IDisposable
                                 // updated orientation rotates that into the right
                                 // world direction toward the target.
                                 rm.Motion.apply_current_movement(cancelMoveTo: false, allowJump: false);
+
+                                // Clamp horizontal velocity so we don't overshoot
+                                // the arrival threshold during the final tick of
+                                // approach. Without this, a 4 m/s body advances
+                                // ~6 cm/tick and visibly runs slightly through
+                                // the target before the swing UM lands.
+                                float arrivalThreshold = rm.MoveToMoveTowards
+                                    ? rm.MoveToDistanceToObject
+                                    : rm.MoveToMinDistance;
+                                rm.Body.Velocity = AcDream.Core.Physics.RemoteMoveToDriver
+                                    .ClampApproachVelocity(
+                                        rm.Body.Position,
+                                        rm.Body.Velocity,
+                                        rm.MoveToDestinationWorld,
+                                        arrivalThreshold,
+                                        (float)dt,
+                                        rm.MoveToMoveTowards);
                             }
                         }
                     }

src/AcDream.Core/Physics/RemoteMoveToDriver.cs

@@ -240,6 +240,58 @@ public static class RemoteMoveToDriver
             originZ);
     }
 
+    /// <summary>
+    /// Cap horizontal velocity so the body lands exactly at
+    /// <paramref name="arrivalThreshold"/> rather than overshooting past
+    /// it during the final tick of approach. Without this clamp, a body
+    /// running at <c>RunAnimSpeed × speedMod ≈ 4 m/s</c> can overshoot
+    /// the 0.6 m arrival window by up to one tick's advance (~6 cm at
+    /// 60 fps) — visible as the creature "running slightly through" the
+    /// player it's about to attack (user-reported 2026-04-28).
+    ///
+    /// <para>
+    /// The clamp is a strict scale-down of the horizontal component
+    /// (X/Y); the vertical component (Z) is left to gravity / terrain
+    /// handling. <paramref name="moveTowards"/> false (flee branch) is a
+    /// no-op since fleeing has no overshoot risk — the body wants to
+    /// move AWAY from the destination.
+    /// </para>
+    /// </summary>
+    public static Vector3 ClampApproachVelocity(
+        Vector3 bodyPosition,
+        Vector3 currentVelocity,
+        Vector3 destinationWorld,
+        float arrivalThreshold,
+        float dt,
+        bool moveTowards)
+    {
+        if (!moveTowards || dt <= 0f) return currentVelocity;
+
+        float dx = destinationWorld.X - bodyPosition.X;
+        float dy = destinationWorld.Y - bodyPosition.Y;
+        float dist = MathF.Sqrt(dx * dx + dy * dy);
+        float remaining = MathF.Max(0f, dist - arrivalThreshold);
+
+        float vxy = MathF.Sqrt(currentVelocity.X * currentVelocity.X
+                             + currentVelocity.Y * currentVelocity.Y);
+        if (vxy < 1e-3f) return currentVelocity;
+
+        float advance = vxy * dt;
+        if (advance <= remaining) return currentVelocity;
+
+        // Already inside or right at the threshold: zero horizontal
+        // velocity, keep Z. (The arrival predicate in Drive() should
+        // have fired this tick, but this is the belt-and-braces guard.)
+        if (remaining < 1e-3f)
+            return new Vector3(0f, 0f, currentVelocity.Z);
+
+        float scale = remaining / advance;
+        return new Vector3(
+            currentVelocity.X * scale,
+            currentVelocity.Y * scale,
+            currentVelocity.Z);
+    }
+
     /// <summary>Wrap an angle in radians to [-π, π].</summary>
     private static float WrapPi(float r)
     {