What is missing is a feasible explanation for how material reactions alone can generate a single entity of conscious awareness.
No, that's not missing - any number of people can see it in that description. You can't accept it; is that a function of an inadequacy of that description, or is that a function of your interpretation?
We can certainly mimic the outward appearance of conscious awareness by complex manipulation of reactions, but there would be nothing within those reactions which constitute the internal conscious awareness which defines "you".
Except that you can't show that there is anything else to it. You keep claiming it, you keep asserting that there must be something else, but you can neither show what it is, show what's missing, or show how there are elements we can see which don't have readily explainable mechanisms. It's like you asserting that a car engine can't be providing the power because dead dinosaurs don't have any explosions in them, but not being able to show where the explosions are coming from somewhere else, that something else is getting into the engine or that the engine isn't doing the work.
The fundamental question here relates to the ultimate source of that which causes manipulation.
No, the fundamental question is what makes you think there's some external 'ultimate source'?
My contention is that your conscious self is the source of manipulation.
No-one is in any doubt what your contention is. However, on an evidentiary basis you have no justification for your contention, and on a philosophical one you have the infinite reduction problem of 'well if your brain needs an external consciousness to drive it, what drives your external consciousness' to try to lever in the untenable 'freedom of will' that you appear to need.
If you relate the source of manipulation to entirely physical causes, then the concept of "you" being the ultimate source disappears into oblivion because physically driven cause and effect chains of reactions will trace back to the beginning of time.
And, again, the issue here isn't the restriction to the physical. Even if, for the sake of argument, we accede to a thought experiment where there's some intangible, separate 'spirit' influencing consciousness, you still have to explain how that is at once dependent on prior events enough to be considered 'will', but unconstrained enough to be considered 'free'. That's not a 'physical' restriction, it's a logical one. The proposal you have, before we get to the mechanics, is logically unsound.
I consider my ability to consciously choose my own thoughts, words and actions to be a reality rather than an illusion, which puts "me" as being the source of manipulation rather than endless chains of physically driven cause and effect.
And your subjective experience is exactly as liable to error as everyone else's subjective experience of everything they do. That's why we measure things, that's why we don't just rely on 'feelings' to determine how the world works.
What is amazing is my ability to consciously interact with this universe rather than just react to it.
What's amazing is your ability to continually fail to react to the points made and continue with the 'but I feel like it' response as though you are making some killer point.
O.
