feat(physics): P5 commit 2 - arm the ConstraintManager leash on accepted positions (#167)

Wire ConstraintManager.ConstrainTo at every current acdream inbound-position
acceptance seam, matching retail SmartBox::HandleReceivedPosition
(0x00453fd0):

- Remote (player + NPC): LiveEntityNetworkUpdateController arms right after
  the hard-teleport branch (remotePlacementRequired) returns - reaching that
  point already means MoveOrTeleport did NOT hard-place - anchored to the
  object's own live IPhysicsObjHost.Position.
- Local player teleport: PlayerMovementController.SetPositionCore now runs
  UnConstrain (retail teleport_hook 0x00514ed0, previously a no-op because
  nothing armed the leash) then re-arms anchored to the just-snapped
  position, composing with the existing StopCompletelyAtPhysicsObjectBoundary
  velocity zero rather than duplicating it. CommitPreparedPosition mirrors
  the same pair for the deferred player-mode-entry commit path.
- Local player ForcePosition: PlayerMovementController.BlipPosition arms
  with NO preceding UnConstrain (retail BlipPlayer/SetPositionSimple
  survives motion/velocity/stick, and the leash is no different).

Push PhysicsBody.IsFullyConstrained from PositionManager.IsFullyConstrained
at the SAME per-tick chokepoint each pump already runs AdjustOffset
(PlayerMovementController.Update, RuntimeRemotePhysicsUpdater.Tick/TickHidden)
so TS-35's read gate in jump_is_allowed sees live state instead of a stub
that is never written.

Tests: local-player arm/teardown/rearm/taper/jump-refusal (Runtime.Tests,
PlayerMovementControllerTests), remote-tick IsFullyConstrained push
(Runtime.Tests, RuntimePhysicsStateTests). Full Core/Runtime/App suites
green with no regressions.

src/AcDream.Runtime/Gameplay/PlayerMovementController.cs

@@ -1288,6 +1288,31 @@ public sealed class PlayerMovementController
     {
         _physics.UpdatePlayerCurrCell(CellId);
         PositionManager?.UnStick();
+        // #167 (Campaign P P5): mirrors the SetPositionCore teleport_hook
+        // teardown+rearm below — see that comment for the retail citation.
+        RearmConstraintLeashAtCurrentPosition();
+    }
+
+    /// <summary>
+    /// #167 (Campaign P P5): retail <c>SmartBox::HandleReceivedPosition</c>
+    /// (0x00453fd0) "Player, teleport-newer" branch re-arms the leash
+    /// immediately after <c>TeleportPlayer</c>'s teardown, anchored to the
+    /// RECEIVED position (here, the body's just-snapped current position).
+    /// Shared by the teleport path (after UnConstrain) and the deferred
+    /// player-mode-entry commit path (<see cref="CommitPreparedPosition"/>),
+    /// which never ran UnConstrain because nothing could have armed the
+    /// leash before the controller had a <see cref="PositionManager"/>.
+    /// docs/research/2026-07-30-constraint-leash-constants.md §2/§3.2.
+    /// </summary>
+    private void RearmConstraintLeashAtCurrentPosition()
+    {
+        if (PositionManager is not { } positionManager)
+            return;
+        AcDream.Core.Physics.Position anchor = _body.CellPosition;
+        positionManager.ConstrainTo(
+            anchor,
+            AcDream.Core.Physics.Motion.ConstraintDistance.GetStartConstraintDistance(anchor.ObjCellId),
+            AcDream.Core.Physics.Motion.ConstraintDistance.GetMaxConstraintDistance(anchor.ObjCellId));
     }
 
     private void SetPositionCore(
@@ -1332,11 +1357,23 @@ public sealed class PlayerMovementController
         _mouseMovementEventPending = false;
         // R5-V3 (#171): retail teleport_hook (0x00514ed0) — PositionManager::
         // UnStick (@0x00514eee) right after the moveto cancel: a teleport
-        // tears down any active stick. (StopInterpolating/UnConstrain have no
-        // armed acdream counterparts — no local-player InterpolationManager,
-        // constraint leash unarmed per #167.)
+        // tears down any active stick. (StopInterpolating has no armed
+        // acdream counterpart — no local-player InterpolationManager.)
+        // #167 (Campaign P P5): teleport_hook's UnConstrain (@0x00514f02) runs
+        // right after UnStick — previously a no-op because nothing armed the
+        // leash. Now that inbound positions arm it (both remote UpdatePosition
+        // and this player teleport/blip path), the teardown must actually run
+        // so a teleport doesn't inherit a stale leash from wherever the player
+        // was constrained before. Retail's "Player, teleport-newer" branch
+        // then immediately RE-arms the leash anchored to the new (received)
+        // position (SmartBox::HandleReceivedPosition 0x00453fd0) — velocity is
+        // already zeroed above by StopCompletelyAtPhysicsObjectBoundary.
         if (publishSharedState)
+        {
             PositionManager?.UnStick();
+            PositionManager?.UnConstrain();
+            RearmConstraintLeashAtCurrentPosition();
+        }
         // Reset the edge tracker: the stop wiped the motion state, so keys
         // still physically held must re-fire as press edges on the next
         // Update (matches the pre-W6 level-triggered behavior of walking
@@ -1367,6 +1404,13 @@ public sealed class PlayerMovementController
         _prevPhysicsPos = pos;
         _currPhysicsPos = pos;
         UpdateCellId(_body.CellPosition.ObjCellId, "force-position");
+        // #167 (Campaign P P5): retail "Player, normal" branch of
+        // SmartBox::HandleReceivedPosition (0x00453fd0) — ConstrainTo anchored
+        // to the received position, with NO teardown call (this is the
+        // BlipPlayer path: motion, velocity, and PositionManager stick
+        // relationships all deliberately survive the blip per the class
+        // comment above, and the leash is no different).
+        RearmConstraintLeashAtCurrentPosition();
     }
 
     private Vector3 ComputeRenderPosition()
@@ -1840,6 +1884,12 @@ public sealed class PlayerMovementController
             // complete Frame after PartArray. Interpolation may replace it;
             // Sticky/Constraint then compose according to their retail rules.
             PositionManager?.AdjustOffset(pmDelta, tickDt);
+            // #167 (Campaign P P5): push the read side of TS-35's
+            // jump_is_allowed gate. MotionInterpreter only has a PhysicsBody
+            // (no host reference), so the per-tick pump — the single owner of
+            // this write, right beside the taper call it mirrors — is the seam
+            // that keeps the stub property current for the local player.
+            _body.IsFullyConstrained = PositionManager?.IsFullyConstrained() ?? false;
             if (pmDelta.Origin != Vector3.Zero)
                 _body.Position += Vector3.Transform(pmDelta.Origin, _body.Orientation);
             if (!pmDelta.Orientation.IsIdentity)