Imo this would be the breakdown:
Declare you use the ready action + pick trigger.
Expend Action for your turn
Expend the associated spell slot
Perform / use up any V, S, M requirements
Finish casting the spell
*Pause*
At this point the spell is cast but the effects, the energy, is being held until released when the designated trigger is met. Once that happens the effects of the spell are released.
This means that you can only use Counterspell when the ready action is taken and the spell is cast, not when it is released later. You can't dispel anything because there's nothing yet to dispel until the spell effects are released. Again Dispel Magic is about targeting the effects, not the spell itself. If concentration is lost, the spell is also lost. This also means that the picking of targets, area the spell will affect, etc.. has not yet happened since the effects of the spell have not yet happened. The only thing that has happened is that the spell has been cast and held before the effects could occur.
Noctem, although our disagreements have been many and public, what might not be obvious is that I also agree with you on many occasions, without feeling the need to construct a post which doesn't add anything except, "Yeah...what
he said".
I agree with your breakdown of the ready action.
(I'll pause now, to let you catch your breath)
I must point out, in support of my points about the cause/effect relationship between 'casting' and 'effect', that readying a spell specifies that you cast a spell normally (meaning: VSM components, slot burned), and that none of the effects occur.
Then, as a reaction, you may release the effect into the world.
Right here, it shows that 'casting' and 'effect' do not overlap.
Zorku has postulated the idea that 'casting' and 'effect' are basically simultaneous. He speculates that the V component is happening continually throughout the duration of the spell effect of
eldritch blast, and at certain points during speaking the magic words of the V component, a beam shoots out.
So, for him, if the verbal component for EB was something like, "Fire one...fire two...fire three...fire four!", then a beam shoots out after each phrase: "Fire one" first beam shoots, "fire two" second beam shoots, "fire three" third beam shoots, "fire four" fourth beam shoots.
This means that, for Zorku, the verbal component and the spell effect are happening simultaneously, with some beams (the spell effect) shooting while the spellcasting (verbal component) has not been completed yet.
And yet, the ready action shows that the 'casting' (VSM components) are
completed, yet the 'effect' (the beams) do not exist in the world until they are released as a reaction, at a later time. This shows both the cause/effect relationship between 'casting' and 'effect', and also that the 'casting' is completed
before the 'effect' begins.
If Zorku was correct, then think about how a readied EB would work. The warlock would have to
complete the V component ("Fire one...fire two...fire three...fire four!"),
before and beams were shot, while at the same time beams were being shot
as soon as the caster said "Fire one...!" and
before the reaction that releases the 'effect' (the beams) into the world.
I don't think that Zorku's circle can be squared, therefore I don't believe that his idea about 'casting' and 'effect' happening side-by-side can possibly be correct.