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 sdcard because then i get the (with sideload e:footer is wrong, e: siganture verification failed or error opening /data/media).

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 sdcard new, but I can't enter a shell command and most badly, I can't enter bootloader.

Please help me guys! :)
Since you can boot into recovery reflash your ROM - make a clean flash (wipe cache , dalvick cache , system and data .

If you can’t flash through twrp , then you have to use the flashtool ...