Pattern: Generic Batching and DeBatching

While we have EDI batching... so of, there are other scenarios where we need to batch and debatch messages. Need to have a pattern than makes this simple to implement, track, and manage for our customers.

No files, tests, or entry points are named. Start by clarifying which non-EDI batching and debatching scenarios are supported, how messages should be tracked, and what customer management means; then locate the relevant accelerator entry points. Done should be a documented, agreed pattern with clear implementation and validation requirements.

Written by the indexing model from the issue text.