But if your emitter emits in every direction (like a lightbulb) and you only catch the ones going in one direction in the sail, you'd propel yourself in that direction.

So having a directional lightsource fire into the sail wouldn't work, but having one that emits light in every direction on one side of the sail would.

So just use a directional light source pointing away from the craft...

Exactly, it is much like using a fan on a boat to blow a sail.

mythbusters were able to show a weird effect where the fan on a boat thing worked - I think they chalked it up to some blown wind from the fan drawing in more than from around the fan..

https://youtu.be/uKXMTzMQWjo?t=75

From a physics point of view it's not like they created an infinite motion machine, the stored energy in the liquid petroleum is being burned, heat from the internal combustion engine radiated into the atmosphere, etc.

It's just converting stored energy (some amount of kJ or kWh in a fuel tank, or battery) into an aerodynamically weird highly inefficient thrust method.

Net effect is not zero if the photon bounces off of the sail

Why use sail then? You can just shoot your photon the opposite way.

That would be a "photon rocket" which is an existing idea, but requires a lot of energy, whereas this uses free energy from the sun.

If it bounces off in the opposite direction then the net effect would be actually be negative.