Set the mode on saved files to a less surprising 644 instead of 777.

[scgtrp]

Also, chmod -x src/document.cpp. My headcanon is that you wrote this file with rehex itself.

[scgtrp]

n.b. in case it wasn't obvious: the mode argument to open() is only used when creating new files, so this does not change the permissions on existing executable files, nor does the current implementation make edited files executable upon saving over them.

My rationale here is that it's highly unlikely that a user creating a new file in a hex editor (on any system more modern than DOS) intended it to be a valid executable for their host system.