Layer exists but I can't change it. selection exists in layer, i can change it, its layer doesn't

[rokosz]

PS CC 2015 Win.

analog image opened as smartobject, 16bit.

I attached a current state of the effort as it pertains to the request.

what i did so far:

I selected a portion of the loaded image, then added a brightness/contrast layer.  made some b/c adjustments. Didn't like the results.

In the past, since I'm ignorant, I would just delete the layer and re-do the selection, re-add the layer.

Tired of doing that,  is there a more elegant way to accomplish this?

I found the Show->Layer edge and the option for extending the selection.

I extended the selection but it doesn't seem  "attached" to the original layer mask (its outside the layer borders). 

I thought no biggie, let me try continuing to adjust the b/c now that I've got an extended selection.

When I click/left or right the b/c layer (any part of it including the thumbnails) I don't get the dialogue for sliding B&C.

I've searched and reviewed helpx subjects but they all seem to be, mostly, refine edge.  Not extend edge, and maintain layer integrity.

Can anyone help or point me at a specific helpx?  thanks.

I found the Show->Layer Edge (blue line).

I also found the option for ?extending selection (I can't spot it now). 

[c.pfaffenbichler]

You might be confusing Layer Masks and Selections. 

If you want to apply the current Selection as the new Layer Mask delete the existing one (Layer > Layer Mask > Delete) and apply it (Layer > Layer Mask > Reveal Selection). (Naturally that’s also possible via the Layers Panel.)