Harden MjrContext cleanup after failed construction

dm_control/mujoco/wrapper/core.py

@@ -619,16 +619,19 @@ def __init__(self,
     if not isinstance(font_scale, mujoco.mjtFontScale):
       font_scale = mujoco.mjtFontScale(font_scale)
     self._gl_context = gl_context
+    self._ptr = None
+    self._gl_context_refcounted = False
     with gl_context.make_current() as ctx:
       ptr = ctx.call(mujoco.MjrContext, model.ptr, font_scale)
       ctx.call(mujoco.mjr_setBuffer, mujoco.mjtFramebuffer.mjFB_OFFSCREEN, ptr)
     gl_context.keep_alive(ptr)
     gl_context.increment_refcount()
+    self._gl_context_refcounted = True
     self._ptr = weakref.ref(ptr)
 
   @property
   def ptr(self):
-    return self._ptr()
+    return self._ptr() if self._ptr is not None else None
 
   def free(self):
     """Frees the native resources held by this MjrContext.
@@ -637,17 +640,24 @@ def free(self):
     necessary. This MjrContext object MUST NOT be used after this function has
     been called.
     """
-    if self._gl_context and not self._gl_context.terminated:
-      ptr = self.ptr
-      if ptr:
-        self._gl_context.dont_keep_alive(ptr)
-        with self._gl_context.make_current() as ctx:
-          ctx.call(ptr.free)
-
-    if self._gl_context:
-      self._gl_context.decrement_refcount()
-      self._gl_context.free()
-      self._gl_context = None
+    gl_context = self._gl_context
+    if gl_context is None:
+      return
+
+    if self._gl_context_refcounted:
+      if not gl_context.terminated:
+        ptr = self.ptr
+        if ptr:
+          gl_context.dont_keep_alive(ptr)
+          with gl_context.make_current() as ctx:
+            ctx.call(ptr.free)
+
+      gl_context.decrement_refcount()
+      gl_context.free()
+      self._gl_context_refcounted = False
+
+    self._ptr = None
+    self._gl_context = None
 
   def __del__(self):
     self.free()

dm_control/mujoco/wrapper/mjr_context_failure_test.py

@@ -0,0 +1,42 @@
+# Copyright 2026 The dm_control Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or  implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ============================================================================
+
+"""Tests cleanup of partially initialized MuJoCo rendering contexts."""
+
+from unittest import mock
+
+from absl.testing import absltest
+from dm_control.mujoco.wrapper import core
+
+
+class MjrContextFailureTest(absltest.TestCase):
+
+  def testFreePartiallyInitializedContextDoesNotReleaseGlContext(self):
+    gl_context = mock.MagicMock()
+    gl_context.terminated = False
+    mjr_context = core.MjrContext.__new__(core.MjrContext)
+    mjr_context._gl_context = gl_context
+    mjr_context._ptr = None
+    mjr_context._gl_context_refcounted = False
+
+    mjr_context.free()
+
+    gl_context.decrement_refcount.assert_not_called()
+    gl_context.free.assert_not_called()
+    self.assertIsNone(mjr_context.ptr)
+
+
+if __name__ == "__main__":
+  absltest.main()