The Plasmoid's Shape Self ability reads, in part:
As a bonus action, you can extrude a pseudopod that is up to 6 inches wide and 10 feet long or reabsorb it into your body. As part of the same bonus action, you can use this pseudopod to manipulate an object, open or close a door or container, or pick up or set down a Tiny object. The pseudopod contains no sensory organs and can’t attack, activate magic items, or lift more than 10 pounds.
One thing that appears to be missing is any reference to casting spells with the range of touch. Barkskin, for example, affects a willing creature, so would be unlikely to qualify as a attack - neither is it activating a magic item or lifting any great weight. Bestow Curse allows for a saving throw, but requires no attack roll on the caster's part, so arguably that isn't an attack either. Shocking Grasp does require a melee spell attack, so that would likely not be an option for the Plasmoid.
Is there a blanket rule I'm missing that covers whether or not plasmoids could use their Shape Self ability to deliver touch spells, or would it be decided on a spell-by-spell basis?