Can you react to Guardian Angel Gear before the recall effect resolves?

No, you cannot react to Guardian Angel before its recall effect resolves.

Here is the breakdown of why:

1. It is a Replacement Effect

As detailed in the RiftJudge FAQs (e.g., FAQ #9811, #8433), Guardian Angel functions as a replacement effect (see Rule 369). Replacement effects do not use the chain and are not abilities that can be reacted to; they intercede during the execution of an event and alter its outcome (Rule 369.1).

2. The Sequence of Events

Because the effect replaces the "death" event with a series of game actions—"kill Guardian Angel instead. Heal me, exhaust me, and recall me"—all of these actions are performed as part of the resolution of that single replacement event.

• No Chain: Because it is a replacement effect and not a triggered ability or spell, it does not go on the chain. There is no point in time where the effect is "waiting to resolve" that would allow you to add a reaction to a chain.
• Atomic Execution: Once the condition for Guardian Angel is met (the unit would die), the replacement effect executes immediately. The unit is healed, exhausted, and recalled to the base as part of that singular, atomic game action.

Summary

Because Guardian Angel is a replacement effect, it does not use the chain. You cannot stop it from resolving once the condition for the unit's death is met, nor can you react to the actions (healing, exhausting, and recalling) it performs as it replaces that death event.