* DWG reader and writer run in a child process (E7)
An allocation failure or stack overflow in the third-party code ends its
process, which catch_unwind can't stop, so one bad file took every open drawing
with it. The app and CLI now run them in a copy of themselves over pipes. A
worker that dies or runs past 30 minutes costs that one open or save. If no
worker can be started, the work stays in the process, as before.
* DWG worker: keep the reply's bytes instead of copying them; skip the test without a bridge