there's currently no way to disable adding the EraseOpenCornersFilter

Currently, it's always added unconditionally when exporting .glyphs to UFOs

https://github.com/googlefonts/glyphsLib/blob/ee5e1fbbde0e40a0352c5c4444e4131020662f6a/Lib/glyphsLib/builder/font.py#L86-L88

Sometime a user may convert their UFOs to .glyphs to do things in it, and then they want to convert them back to UFOs without that filter messing with their outlines. We need to provide a way to disable it.

see https://github.com/googlefonts/fontmake/issues/897 for related discussion

Start in Lib/glyphsLib/builder/font.py at lines 86-88, where EraseOpenCornersFilter is added during .glyphs-to-UFO export. Read the export options and the related fontmake issue to determine how disabling should be exposed. Done means users can convert UFOs without the filter while existing exports retain current behavior.

Written by the indexing model from the issue text.