Action or javascript; how to program "escape key"

@contactzero  Perhaps a .confirm() and conditional script step could offer the choice of running the free transform or to play the canvas action instead? This way you avoid the issue of having the transform already set and then needing to escape it.

From a "big name" scripter, I have the quote, "It’s not possible to send keys with a PS script."

I think I do understand the problem, as I try a lot of this cool stuff myself.

I use an external helper for some of this (for PC that would be a small AutoIt.exe that's running in the background, although sometimes I open another one from within an action.).

I will give one example that might help you. Let's say you have F1 programmed as your Run/Continue key for actions (that's what I do). Now, in your helper app you could catch the F1 key and do something else first, like ESC.

To put it very simply, F1 would call this function...

Func F1_was_Pressed()								; 	 
 If WinActive("[CLASS:Photoshop]") Then
    Send("{ESC}")										 				 
    Sleep(300)
    Send("{F1}")
  EndIf
EndFunc

This can of course cancel out things when you don't want it to..., so further thought or intelligence could be needed. Probably not handy on a key you use all the time, like Run/Continue, but on a key that saves your document, for example (to make sure you have left all fields and the key actually engages).

To have someone clicking on an action would be different though... If these actions are always in the same spot, maybe you could have the helper app go to a function depending on where you clicked on the screen. It could possibly intercept the click, do ESC first, then send the real click that runs the action underneath. I'm 99% sure this is possible with this kind of software, and I'm probably doing it somewhere.

For some UI elements, you can detect and decide based on the internal code for that element. This makes it possible to deselect a field, do something, then make that field active again, for example.

In my Mac days 25 years ago, I used QuicKeys. I don't know what's the best one at the moment...

Update:
I just checked if AutoIt can pick up an individual ID or text for each action button, and seems it can't — just cursor coordinates and the color underneath (meaning, your critical actions would have to be in a ±exact spot for the coordinates method to work).

I can't think of a way to catch the ESC key in an Action, but in ExtendScript (JavaScript) you can...

if (ScriptUI.environment.keyboardState.keyName == "Escape") {
    // ESC key has been pressed
}

Only the Free Transform seems of interest to me and I am not sure I understand the issue. 

Do you want to allow for user interaction? 

If so the user pressing enter to confirm the transformation seems perfectly reasonable and that can be done when executing the AM-code of the operation with »DialogModes.ALL«. 

Maybe you should explain what you are actually trying to achieve and post screenshots to illustrate.