Transitions

A Sectile transition receives immutable semantic state and a semantic event. It returns either a complete next state with ordered commands or a typed failure.

applyEvent : State × Event
  → Result<State × OrderedCommand*>

Transition guarantees

• Deterministic: equal state and input produce equal output.
• Pure: applying an event performs no host side effect.
• Atomic: a successful transition exposes one complete next state.
• Failure-atomic: a rejected transition leaves state and commands unchanged.
• Ordered: commands preserve a defined execution order.
• Bounded: event work is constrained by the model's resource ceilings.

Commands

Commands describe required host work without executing it inside core state.

focus · scroll · announce · activate · request · clipboard

An adapter interprets those commands for its environment. This keeps a DOM focus request and a terminal cursor request observably equivalent at the semantic layer while allowing different host operations.

Revision

Controlled and asynchronous hosts can wrap state in a revision snapshot.

RevisionSnapshot<State> = {
  revision: Natural
  state: State
}

An accepted event increments the revision exactly once. A stale or invalid event preserves the current revision and state and emits no commands. Accepted boundary no-ops still advance the revision, distinguishing a handled event from unhandled input.

Atomic composition

Independent child transitions compute their candidate results first. The composite commits only when every child succeeds, then concatenates commands in a fixed order. No partial child state becomes observable.