Set nativeccd as default.

PiperOrigin-RevId: 731343200
Change-Id: I315779017b676f3d118e0d38ee53a515272f50b8

doc/XMLreference.rst

@@ -582,6 +582,12 @@ from its default.
    This flag disables the mid-phase collision filtering using a static AABB bounding volume hierarchy (a BVH binary
    tree). If disabled, all geoms pairs that are allowed to collide are checked for collisions.
 
+.. _option-flag-nativeccd:
+
+:at:`nativeccd`: :at-val:`[disable, enable], "enable"`
+   This flag enables the native convex collision detection pipeline instead of using the
+   `libccd library <https://github.com/danfis/libccd>`__, see :ref:`convex collisions<coCCD>` for more details.
+
 .. _option-flag-eulerdamp:
 
 :at:`eulerdamp`: :at-val:`[disable, enable], "enable"`
@@ -635,14 +641,12 @@ from its default.
 
 .. _option-flag-multiccd:
 
-:at:`multiccd`: :at-val:`[disable, enable], "disable"` |nbsp| |nbsp| |nbsp| (experimental feature)
+:at:`multiccd`: :at-val:`[disable, enable], "disable"`
    This flag enables multiple-contact collision detection for geom pairs that use a general-purpose convex-convex
-   collider e.g., mesh-mesh collisions. This can be useful when the contacting geoms have a flat surface, and the
+   collider e.g., mesh-mesh collisions. This can be useful when the contacting geoms have a flat surface and the
    single contact point generated by the convex-convex collider cannot accurately capture the surface contact, leading
-   to instabilities that typically manifest as sliding or wobbling. Multiple contact points are found by rotating the
-   two geoms by ±1e-3 radians around the tangential axes and re-running the collision function. If a new contact is
-   detected it is added, allowing for up to 4 additional contact points. This feature is currently considered
-   experimental, and both the behavior and the way it is activated may change in the future.
+   to instabilities that typically manifest as sliding or wobbling. The implementation of this feature depends on the
+   selected convex collision pipeline, see :ref:`convex collisions<coCCD>` for more details.
 
 .. _option-flag-island:
 
@@ -652,12 +656,6 @@ from its default.
    allows for `island visualization <https://youtu.be/Vc1tq0fFvQA>`__.
    In a future release, the constraint solver will exploit the disjoint nature of constraint islands.
 
-.. _option-flag-nativeccd:
-
-:at:`nativeccd`: :at-val:`[disable, enable], "disable"`
-   This flag enables the native convex collision detection pipeline instead of using the
-   `libccd library <https://github.com/danfis/libccd>`__.
-
 .. _compiler:
 
 **compiler** (*)
@@ -6977,16 +6975,11 @@ pipeline. These 3 sensors share some common properties:
    to geom-geom penetration) will be reported by :ref:`sensor/distance<sensor-distance>`.
    In order to determine collision properties of non-penetrating geom pairs, a positive :at:`cutoff` is required.
 
-   .. admonition:: Positive cutoff values
+   .. admonition:: different (correct) behavior under `nativeccd`
       :class: note
 
-      .. TODO: b/339596989 - Improve mjc_Convex.
-
-      For some colliders, a positive :at:`cutoff` will result in an accurate measurement. However, for collision
-      pairs which use the general ``mjc_Convex`` collider, the result will be approximate and likely inaccurate.
-      This is considered a bug to be fixed in a future release.
-      In order to determine whether a geom pair uses ``mjc_Convex``, inspect the table at the top of
-      `engine_collision_driver.c <https://github.com/google-deepmind/mujoco/blob/main/src/engine/engine_collision_driver.c>`__.
+      As explained in :ref:`Collision Detection<coDistance>`, distances are inaccurate when using the
+      :ref:`legacy CCD pipeline<coCCD>`, and its use is discouraged.
 
 :at:`geom1`, :at:`geom2`, :at:`body1`, :at:`body2`
    For all 3 collision sensor types, the two colliding geoms can be specified explicitly using the :at:`geom1` and