Timing of revealing agents

[Konrad Klar]

You may turn any of your face-down agents face-up (i.e., reveal them) at any time
during your opponent’s movement/hazard phase. This doesn’t count as an agent
action as outlined above and it doesn’t count against the hazard limit. Alternatively,
you must reveal an agent when it attacks, when it makes an influence attempt, or
when certain cards are played.

Preasumably if hazard requires an agent of specific abilities and/or at specific site, the anet must be revealed at declaration (to verify validity of the declaration).

But what about revealing an agent not due of playing a hazard? Is it an immediate action or it must be declared and resolved in chain of effect?

Hazard player may want to reveal an agent in response to We Have Come To Kill/A Chance Meeting, to prevent his opponent from playing the agent as character.
If revealing is immediate action, opponent may respond with Withdrawn To Mordor, otherwise not.

[Bandobras Took]

I believe it is not an "agent action" but is nevertheless an action for the purposes of timing when revealing an agent for its own sake (similar to the the difference between tapping a Nazgul for effect text and tapping and discarding to sideboard).

If revealing is the requirement for another action, then it is the active condition for such and occurs instantly.

Thus a chain would go either:

Declare
Player A: WHCtK
Player B: Reveal
Player A: Cannot play withdrawn yet because declaration of revealing the agent has not resolved.

Resolve
B: Agent is now revealed
A: WHCtK performs its usual crap, which I'll shut up about in order to not derail the thread

or:

Declare
Player A: WHCtK
Player B: Reveal as condition of Will You Not Come Down or another non-attack creating card
Player A: Withdrawn

Resolve
Player A: Withdrawn resolves and sends agent packing
Player B: Hazard used in conjunction with revealing agents fizzles
Player A: WHCtK resolves