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I don't think level 4 is possible. There are three total unblocked paths to the bottom two delivery slots (allowing down-up-down delivery), but the exit is outside this area, meaning you need down-up-down-up.

Unless I'm missing some new mechanic, that lone tree makes it impossible.

It's possible (and you're probably missing a new mechanic). Rot13 hints with increasing spoilery:
1.) Gurer'f zber crbcyr guna qrfgvangvba fybgf.
2.) Lbh pna fbzrubj pneel gjb cnffratref.
3.) Gel ehaavat bire n cnffratre.
4.) Lbh arrq gb pneel 2 cnffratref jura tbvat haqre gur fybgf.