Not naive at all. I didn't word my question well as my interest is broadly if this new technology gives us any more ability to differentiate the delivery, either by selecting for cancer cells or by only 'activating' within cells that are cancerous.

In general there are a number of 'targeted' therapies being developed that don't specifically target the cancer cell, but try to make life more difficult for the cancer by broadly impacting a cell's ability to hide, replicate and accumulate...features that the rest of a healthy human tissue is less dependent upon.

I'd prefer to have the poison not have to be in the same process as the detection? The detector likely needs to enter or interact with the cell regardless of whether it's cancerous

One version of what you are describing is called an antibody-drug conjugate. There are about a dozen ADCs approved and many more in various stages of development