Channel contract that groups several same-scope Timeline Channels into one union channel. A Composite Timeline Channel matches when any referenced child channel would accept the delivered event. It is useful when a workflow should react to a family of participant timelines while binding handlers to one logical channel key. This type does not create global consensus and does not collapse the child timelines into one storage log. Each child timeline retains its provider, checkpoint, completeness, actor attribution, and trust model. The composite only simplifies routing inside the document. A correct feeder/processor must still preserve deterministic ordering across the relevant timelines using provider completeness guarantees and the Blue Contracts checkpoint model.