Guard host transfers inside pure_callbacks from deadlocking the TPU.

Also fix python/callback.cc to not swallow errors in numpy conversions.

PiperOrigin-RevId: 619375128

tests/python_callback_test.py

@@ -797,6 +797,20 @@ def f(x):
     with self.assertRaisesRegex(Exception, "Errors should propagate."):
       print(np.array(f(2.0)), flush=True)
 
+  @unittest.skipIf(xla_extension_version < 250, "jaxlib version too old")
+  def test_reentrant_error_propagation(self):
+    reentrant_fn = jax.jit(jnp.sin).lower(2.0).compile()
+
+    @jax.jit
+    def f(x):
+      return jax.pure_callback(reentrant_fn, x, x)
+
+    try:
+      np.array(f(2.0))
+    except:
+      # Only should not deadlock.
+      pass
+
   def test_can_take_grad_of_pure_callback_with_custom_jvp(self):
 
     @jax.custom_jvp