Proposal: explicit DSL API to cancel pending dispatches

[hkusu]

Summary

Introduce an explicit API in the Store {} DSL to cancel pending/queued dispatches from inside handlers.

This is an alternative (or complement) to policy-based behavior discussed in #164.

Motivation

In some flows, the app should explicitly discard already-queued actions at a specific point (for example, after reaching a terminal state or after handling a one-shot action).

A local, explicit DSL call can be easier to reason about than only having a global queue policy.

Proposal

Add a function available from relevant DSL scopes:

• Preferred name: cancelPendingActions()
• Alternative names: cancelQueuedDispatches(), clearActionQueue()

Example

state<MyState.Active> {
    action<MyAction.Finish> {
        cancelPendingActions()
        nextState(MyState.Done)
    }
}

Relationship to #164

• Related issue: #164 Proposal: pending dispatch policy on state transitions
• Proposal: pending dispatch policy on state transitions #164 focuses on queue policy during state transitions.
• This issue proposes an explicit API that can be called at the exact point where cancellation is needed.

Both approaches could be implemented independently or combined.

[hkusu]

Resolved in #172