Respond to first batch of reviewer comments

Author: timsaucer

docs/source/user-guide/io/distributing_work.rst

@@ -92,10 +92,16 @@ Then build the expression in the driver and fan it out:
         )
     print(results)  # [[2, 4, 6], [20, 40, 60]]
 
-When saved to a ``.py`` file and executed with the ``spawn`` or
-``forkserver`` start method, wrap the driver block in
-``if __name__ == "__main__":`` so worker processes can re-import the
-module without re-running it.
+.. note::
+
+   When saved to a ``.py`` file and executed with the ``spawn`` or
+   ``forkserver`` start method, wrap the driver block in
+   ``if __name__ == "__main__":`` so worker processes can re-import
+   the module without re-running it. This is a standard Python
+   :py:mod:`multiprocessing` requirement, not DataFusion-specific —
+   see `Safe importing of main module
+   <https://docs.python.org/3/library/multiprocessing.html#the-spawn-and-forkserver-start-methods>`_
+   in the Python docs.
 
 
 What travels with the expression

examples/multiprocessing_pickle_expr.py

@@ -17,6 +17,10 @@
 
 """Distribute different DataFusion expressions to worker processes.
 
+For background — the shipped-expression model, what travels inline vs
+by name, portability requirements, and the security threat model —
+see ``docs/source/user-guide/io/distributing_work.rst``.
+
 Builds a list of parametric expressions in the driver — each closing
 over a different threshold value — ships one per worker via
 ``multiprocessing.Pool``, and collects the results back. The closure

examples/ray_pickle_expr.py

@@ -17,6 +17,10 @@
 
 """Distribute DataFusion expressions to Ray actors.
 
+For background — the shipped-expression model, what travels inline vs
+by name, portability requirements, and the security threat model —
+see ``docs/source/user-guide/io/distributing_work.rst``.
+
 Build an expression in the driver, ship it to a pool of Ray actors, and
 have each actor evaluate it against its own slice of data. Python UDFs
 travel with the shipped expression — no actor-side registration needed.