KeepLastOutput

A decorator that remembers the last output produced by the inner stage and re-emits it when the inner stage yields no value.

The decorator has two internal states:

• None state (initial): no output has been seen yet. The inner stage's h8io.stages.Yield.None is forwarded unchanged; a h8io.stages.Yield.Some is forwarded and transitions the wrapper to the Some state.
• Some state: a previous output out is remembered, so the wrapper always emits a value. A new h8io.stages.Yield.Some from the inner stage is forwarded as is and updates the remembered value; on h8io.stages.Yield.None the remembered value is emitted instead.

In both states the evolution is mapped so that continuations remain wrapped in the appropriate KeepLastOutput variant, preserving the last-value semantics.

Both variants are internal to the package: the decorator is reached through the KeepLastOutput.apply factory, which always starts in the None state, and the state it is in afterwards is not part of the API.