Set MJX minimum friction value to mjMINMU.

PiperOrigin-RevId: 783381620
Change-Id: I353a4fa39956ecb0ed0e1b2bbcaff651e8c68606

mjx/mujoco/mjx/_src/collision_driver.py

@@ -271,7 +271,7 @@ def _contact_groups(m: Model, d: Data) -> Dict[FunctionKey, Contact]:
       # pair contacts get their params from m.pair_* fields
       params.append((
           m.pair_margin[ip] - m.pair_gap[ip],
-          m.pair_friction[ip],
+          jp.clip(m.pair_friction[ip], a_min=eps),
           m.pair_solref[ip],
           m.pair_solreffriction[ip],
           m.pair_solimp[ip],
@@ -321,7 +321,7 @@ def _contact_groups(m: Model, d: Data) -> Dict[FunctionKey, Contact]:
         pos=None,
         frame=None,
         includemargin=includemargin,
-        friction=jp.maximum(friction, mujoco.mjMINMU),
+        friction=friction,
         solref=solref,
         solreffriction=solreffriction,
         solimp=solimp,