NS-23: unstuck bump top — descend steers xz to goal; doc abs(dy)

Server already allows downward steps via abs(ΔY) vs MaxVerticalStep; document
that explicitly.

Client: when authoritative goal Y is below the body, skip nav waypoints and
steer horizontally toward the goal only — mesh waypoints under the rim
gave ~no horizontal speed (felt like wrong collision).

client/scripts/player.gd

@@ -6,12 +6,15 @@ extends CharacterBody3D
 ## and steps comes from `move_and_slide` + floor_* on CharacterBody3D. Move **legality** (step,
 ## distance, bounds) is server MoveCommand only — not reimplemented here.
 ##
-## NavigationAgent3D detours obstacles; steering uses target **xz** only.
+## Nav detours except when goal Y is below us: then xz toward goal (waypoints sit under bump rims).
 
 const MOVE_SPEED: float = 5.0
 const ARRIVE_EPS: float = 0.35
 const VERT_ARRIVE_EPS: float = 0.055
 const DIRECT_APPROACH_RADIUS: float = 0.85
+## Server goal clearly below us (descending). Nav mesh waypoints are often under the rim first;
+## steering at next gives almost no horizontal speed — walk out on xz toward the authorized goal.
+const DESCEND_GOAL_Y_MARGIN: float = 0.06
 
 var _has_walk_goal: bool = false
 var _auth_walk_goal: Vector3 = Vector3.ZERO
@@ -73,6 +76,11 @@ func _physics_process(_delta: float) -> void:
 		move_and_slide()
 		return
 
+	if _auth_walk_goal.y < global_position.y - DESCEND_GOAL_Y_MARGIN:
+		_set_horizontal_velocity_toward(_auth_walk_goal)
+		move_and_slide()
+		return
+
 	if horiz_dist <= DIRECT_APPROACH_RADIUS:
 		_set_horizontal_velocity_toward(_auth_walk_goal)
 	else:

server/NeonSprawl.Server/Game/PositionState/MoveCommandValidation.cs

@@ -4,6 +4,8 @@ namespace NeonSprawl.Server.Game.PositionState;
 /// <remarks>
 /// <para><b>Precedence</b> when multiple rules fail: <see cref="MoveCommandReasonCodes.HorizontalStepExceeded"/>,
 /// then <see cref="MoveCommandReasonCodes.VerticalStepExceeded"/>, then <see cref="MoveCommandReasonCodes.OutOfBounds"/>.</para>
+/// <para>Vertical uses <c>abs(ΔY)</c>, so <b>descending</b> (target Y lower than current) is allowed when the
+/// drop is within <see cref="MovementValidationOptions.MaxVerticalStep"/> — same as climbing.</para>
 /// </remarks>
 public static class MoveCommandValidation
 {