Debounced

Opt-in marker for an Effect whose async dispatch should cancel any previous in-flight async effect for the same chat with an equal debounceKey, instead of letting them run concurrently — e.g. a user clicking through categories quickly, where only the latest fetch's result should matter.

Only has an effect on effects registered via EffectRegistry.registerAsync (see AsyncEffectHandler); ignored for synchronous effects. Not implementing this interface is the default and means "run every dispatch of this effect independently" — cancellation is never automatic or implicit for effects that don't opt in.