feat(physics): R5-V4 behavioral slice — head stance dispatch (all mt) + #164 autonomy bit + mt-0 wire flags

Three unpack_movement parity items (facade deferred per the handoff's
own optional clause — see r5-wiring-handoff §V4 status):

1. HEAD style-on-change (0x00524440 @00524502-0052452c): both GameWindow
   routing heads (remote + player) now dispatch DoMotion(style, ctor
   defaults) when the UM's stance differs from the interp's current
   style, BEFORE the movement-type routing — for EVERY type. Previously
   style applied only through the mt-0 funnel copy, so a chase/turn UM
   (mt 6-9) carrying a stance change started the move in the OLD stance
   (a monster charged in NonCombat posture until the next mt-0). The
   RetailObserverTraceConformanceTests exclusion note updated — the
   trace filter stays (head calls can't appear in a
   MoveToInterpretedState replay) but the production gap it pointed at
   is closed.

2. #164 (closes): the action-replay loop threads each action's autonomy
   into the dispatch params (Autonomous = the 0x1000 splice, raw
   305982) — replayed actions enter the interpreted actions list with
   their real autonomy instead of ctor-default false.

3. mt-0 wire flags consumed (UpdateMotion parsed them since R4-V3):
   0x1 StickToObject → CPhysicsObj::stick_to_object port (0x005127e0:
   resolve target, PartArray radii — 0 when shapeless, guid-as-is for
   acdream's flat entity table — → PositionManager.StickTo; unresolvable
   target → no stick), at BOTH case-0 tails in retail order
   (@00524583-0052458e: funnel apply → stick → longjump flag);
   0x2 StandingLongJump → Motion.StandingLongJump, UNCONDITIONAL write
   (absent flag clears — retail @0052458e). ServerMotionState gains the
   StandingLongJump field.

Conformance: ChaseArm_WithStanceChange_AppliesStanceBeforeTheChase
(harness mirrors the routing-head dispatch) +
Actions_ReplayCarriesAutonomyIntoTheInterpretedList. Suite 4041 green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.Core.Tests/Physics/Motion/RemoteChaseEndToEndHarnessTests.cs

@@ -251,11 +251,22 @@ internal sealed class RemoteChaseHarness
         bool sticky = false,
         bool useSpheres = false,
         float targetRadius = 0f,
-        float targetHeight = 0f)
+        float targetHeight = 0f,
+        uint wireStance = 0u)
     {
         Interp.InterruptCurrentMovement?.Invoke();
         Interp.UnstickFromObject?.Invoke();
 
+        // R5-V4a: the unpack_movement HEAD style-on-change (GameWindow's
+        // routing-head mirror — 0x00524440 @00524502-0052452c): fires for
+        // EVERY movement type, BEFORE the type routing, on CHANGE only.
+        if (wireStance != 0u)
+        {
+            uint wireStyle = 0x80000000u | wireStance;
+            if (Interp.InterpretedState.CurrentStyle != wireStyle)
+                Interp.DoMotion(wireStyle, new MovementParameters());
+        }
+
         var mp = new MovementParameters
         {
             CanWalk = true,
@@ -871,4 +882,47 @@ public sealed class RemoteChaseEndToEndHarnessTests
             $"chase did not re-stick after the re-arm; mt={h.Mgr.MovementTypeState} " +
             $"dist={h.DistToPlayer:F2}");
     }
+
+    /// <summary>
+    /// R5-V4a: the unpack-head style-on-change — a chase arm (mt-6) whose UM
+    /// carries a CHANGED stance applies the stance FIRST (retail
+    /// unpack_movement @00524502-0052452c dispatches DoMotion(style) before
+    /// the movement-type switch), so the creature draws into Combat and THEN
+    /// runs — instead of chasing in the old NonCombat stance until the next
+    /// mt-0 UM. Closes the RetailObserverTraceConformanceTests "S3 wires the
+    /// unpack-level style-on-change" exclusion's production gap.
+    /// </summary>
+    [Fact]
+    public void ChaseArm_WithStanceChange_AppliesStanceBeforeTheChase()
+    {
+        var h = new RemoteChaseHarness(_out);
+        h.PlayerPos = new Vector3(0f, 12f, 0f);
+        h.PlayerVelocity = Vector3.Zero;
+
+        // settle in NonCombat — NO prior stance UM (the pre-V4 gap: nothing
+        // but an mt-0 could change the stance).
+        for (int i = 0; i < Seconds(0.5f); i++) h.Tick();
+        Assert.Equal(RemoteChaseHarness.NonCombat, h.Seq.Manager.State.Style);
+
+        // the arm carries the Combat stance in its UM header (mt-6).
+        h.UmMoveToObject(wireStance: RemoteChaseHarness.Combat & 0xFFFFu);
+
+        // the stance adopts at the head — before any chase motion completes.
+        Assert.Equal(RemoteChaseHarness.Combat, h.Interp.InterpretedState.CurrentStyle);
+
+        // ...and the chase still installs its forward cycle normally, now in
+        // the Combat style family.
+        int installTick = -1;
+        for (int i = 0; i < Seconds(6f) && installTick < 0; i++)
+        {
+            h.Tick();
+            if (h.Seq.Manager.State.Substate == RemoteChaseHarness.Run
+                || h.Seq.Manager.State.Substate == RemoteChaseHarness.Walk)
+                installTick = i;
+        }
+        Assert.True(installTick >= 0,
+            $"forward cycle never installed after the stance-carrying arm; " +
+            $"mt={h.Mgr.MovementTypeState} substate=0x{h.Seq.Manager.State.Substate:X8}");
+        Assert.Equal(RemoteChaseHarness.Combat, h.Seq.Manager.State.Style);
+    }
 }