robot game - Drop Bricks (concept stage)

I want to build a 'robot game' using arduino as the controller.
The project will include at its core a manueverable claw and conveyor belt.

What I'm having a problem figuring out is I need a cube with a male and
female connector on 3 of its 4 sides.
So that if I have two of them, pushing them together on any of the three
sides will make them stick.
And they can only become unstuck and will be instantly detached when the robot arm chooses it.
(possibly by: needle is stabbed into the centre of either one of the cubes.)
I figured a pressure sensitive switch would work.
But how would the connectors be made?

The robot collects the cubes, detaches and removes them.
Does anyone know of an alternative to a laser designator?

I thought of using a weight sensor to tell the arm which cubes to collect.

feasibility?

I don't understand everything.
Your robot collects cubes, and would be able to attach them to each other ?
And the connector should pop off, with some switch ?
But then you write about seven rows ?

I don't know any switch with an actuator to release the connection.
I even wonder if this project can be done.
Is there an other way to connect and release the cubes ?

manueverable claw, conveyor belt, needle and “toy” = uninsurable

yes the robot collects cubes.
And should be able to somehow connect and disconnect cubes to each other.

Robot creates a predefined shape by attaching cubes together.
Then loads the shape onto the belt.

Robot nudges the shape from side to side, when told to by the player.

When a row of cubes reaches from one side to the other, the robot must disconnect those cubes and remove only those cubes.

Magnets seem to be the most obvious solution, although I suppose you might be able to get a three dimension ‘lego brick’ design to work. Any thought on how big these cubes will be, and how heavy, and how much time/money you’re willing to spend on them, and how many you’ll have, and what sort of forces you’ll be able to apply to assemble and dismantle your connected blocks?