Extension over modification.
Keep local process logic in a governed extension layer when it does not belong inside the system of record.
Operating pattern
A core platform can reach the boundary of its standard functionality while a business process still needs specialized behavior. Putting that behavior directly into the core makes the local requirement part of every future core change.
The architectural question is not whether the requirement is valid. It is where the requirement belongs and how it should connect to the system of record.
Capability pattern
Define an explicit decision boundary for extension work. Necessary process logic is placed in a side-by-side extension, connected through governed interfaces, while canonical transactions and records remain in the core.
Document the boundary, the owner, the integration contract, and the conditions that would move logic back to standard platform functionality.
What the pattern enables
The pattern connects decision rights and workflows. Teams can evaluate each request against the same extension criteria, and the resulting workflow has a defined relationship to the core system, its data, and its controls.