= Solution
The pipe <object interface> supports \b[<command-query separation>]: consuming an input changes state, while querying the result observes the current output without feeding another input. A client can inspect the result repeatedly, including an initial result when the concrete pipe defines one. That is useful for accumulated statistics.
The channel <object interface> instead packages an input update and its associated output into one call. For request-and-result processing this is simpler: the caller cannot forget which update precedes a query. A pipe caller must respect the intended order of operations, and interleaving other callers between consume and result can change the observation. A single channel <object method> is not automatically thread-safe either; synchronization is a separate property.
\b[Neither <object interface> is universally better.] The choice depends on whether clients need independent observation of state or a combined transformation step. The adapters below can reconcile their protocols, provided the initial-result policy is made explicit.
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