nostr:npub1nd396e8flpwdgzrxmu5n3eat0nv4a35zqs84avm3xskurpxld76qh3s249
The script comes from the Android Open Source Project. It wasn't written by GrapheneOS. It's the same flashing script used for the Pixel stock OS factory images and other devices.
GrapheneOS has fixed multiple issues with it including not handling spaces in the path, missing device model check, missing fastboot version check on Windows, unsafe handling of firmware flashing when mixed with anti-rollback fuses, erasing additional persistent state, etc. We didn't redo the rest of it yet.