Gonna jump in and clarify the issue a little bit.
I believe the only free action spells we currently have are in Gear Up and the Strategist's Helm.
To me the question boils down to how these free actions are treated. Are they treated A) as normal spells, with steps that can be interrupted, or B) as instantaneous effects, i.e. inside Gear Up's "Resolve Spell" step, in case of the Helm: Instantaneous in priority like Hand of Bim.
In our game we resolved it as in option A, which is probably right, but on the other hand the rule is that you can't interrupt an initiated step, and I feel like we are interrupting Gear Up's "Resolve Spell" step, since that shouldn't be over before the free actions are resolved.
If B, then you would have to reveal DI to break Gear Up and the whole process stops with just 2 mana and Gear Up lost. Much simpler!
Going further with option A: If possible to interrupt free action #1, what happens to free actions #2 and #3.
- Are they lost too?
- Does it just stop Gear Up (meaning the other spells stay in book), or
- does it allow free action #2 and #3 to be cast after #1 is broken?