ReadonlybranchBranch member ids in declaration order.
ReadonlydeciderDecider / selector stage id.
Optional ReadonlydefaultDefault branch id when set via .setDefault(); undefined when
no default is configured (e.g., selectors).
ReadonlytypeSpec type ('decider' vs 'selector') — exposed so consumers
don't need to look up the original onStageAdded event.
Event payload for
StructureRecorder.onDeciderComplete. Fires when a decider / selector sub-builder closes via.end(). By the time this fires every branch has been announced and thedefaultBranch(if set via.setDefault()) is final. Lets recorders treat the decider as no-further-mutation and snapshot its branch list as final.