`adb shell` returns with error: closed

I somehow bricked my OnePlus One phone badly. It only loads directly to the recovery. Pressing vol up + power button or rebooting it with adb reboot bootloader doesn't get me to the bootloader. I think I erased the bootloader partition or deleted my bootloader. Here comes the tricky part. I can't even sideload any file or access my internal SD card because then I get either following error messages: - E: footer is wrong - E: signature verification failed - Error opening '/data/media' (no such file or directory) Right now I can either flash the OnePlusRestoreTool(64GB) recovery or the ColorOS recovery tool (both can't access the internal storage - button is not clickable). I thought I just have to mount my SD card new, but I can't enter a shell command, and most badly, I can't enter the bootloader. How to fix it?