Do not mark notification work complete with no selected channels

A notification dispatcher can falsely report completion when its selected channel set is empty: a completion predicate that requires every selected channel to be terminal succeeds without examining any delivery state. This is especially easy to miss when a general notification default names a channel that the specialized dispatcher filters out. Validate channel configuration explicitly and expose disabled or misconfigured processing separately from dispatched or finished outcomes. Preserve pending durable work until a supported channel actually claims and settles it. Recovery queries must also make the empty-channel case observable. This diagnosis establishes skipped provider attempts; it does not establish recipient validity or provider failure.

Applies when: A specialized notification worker filters a shared channel configuration and uses aggregate completion checks. Keywords: notifications empty channels vacuous completion pending dispatch configuration recovery