Channel contract that accepts Timeline Entry events for a configured timeline. Timeline Channel is the scope-local runtime entry point that lets a Blue document react to messages stored in append-only timeline infrastructure. The channel identifies which timeline it observes, usually through `timelineId` and concrete provider fields. It does not define the provider protocol by itself. A feeder or provider integration is responsible for fetching entries, obtaining completeness or finality guarantees, deduplicating through checkpoints, and delivering entries in a deterministic order. Once an entry is delivered, the channel can expose the entry or its `message` as the payload for same-scope handlers. Timeline Channel must not be confused with the Timeline. The Timeline is storage and attribution infrastructure; the channel is a contract inside one Blue document. Multiple documents may observe the same timeline, and one document may observe many timelines. The channel does not make the provider understand the document's semantics. It simply defines how attributed timeline entries enter the processor.