The core rulebook states on p129, under Weapon Special Qualities:

Snare
Weapons with this quality are designed to entangle enemies.
On a successful hit, the target must make an Agility Test or be immobilised. An immobilised target can attempt no other actions except to try to escape the bonds. He can attempt to burst the bonds (a Strength Test) or wriggle free (an Agility Test) in his Turn. The target is considered helpless until he escapes.

My question is this: How strictly do you interpret "no other actions"? Could a psycher use a focus power? The player would argue: I lie completely still, make no attemt to escape, and use xxxx". Could a tech-priest activate implants, such as Luminen Shock?

By the text, no they can't. But it seems a little strange. There is a similar wording to the grapple-process also, saying if you're grappled you may not do anything except trying to escape the grapple. How do you handle this? The Luminen Shock seems like it was designed exactly for grapple-situations.

Darth Smeg said:

I would consider it a panic response that restricts your actions.

Although it hasn't come up, I would go with attempting to do anything other than escape would require a -30 or more Willpower test depending on the action. A snare weapon isn't going to be gentle, forgiving, or comfortable.

Common Sense says it only restricts bodily actions. Its so obvious that the rules writer probably never though of this needing to be explicitly written down.

Manifesting Psy Powers is a "purely mental action". Also the activation of many cyber-implants is purely mental, too. Like using an implanted Voxcaster, or using your Chemgland-Implant.

If reading a rule with Common Sense leads to realistic, probably outcomes on the one hand, and reading it 110% litterally leads to preposterous outcomes, then its clear how it should be read.

Highly suspicious that you're asking about this in the contest of Psykers and Tech Priests Darth Smeg, I pleasantly remeber a couple of threads dedicated to these sorts of nefarious schemes. Mwah ha ha...

Good to see you're keeping up the pressure on the freakazoids.