Change Service Overview (Group 9)
The live denomination-management surface for making change, reserving serial numbers, breaking value, and joining value.
Overview
Group 9 handles denomination conversion workflows. The audited live surface includes both the older break/join building blocks and the top-level make_change command.
Per-command pages: 90 make_change, 91 get_available_change_sns, 92 break, and 93 join.
When to use which command
Reach for make_change when the client wants change without manually driving every lower-level step. Use get_available_change_sns as the inventory/discovery step before break or join. Use break to split a larger denomination into smaller ones with direct control over the conversion. Use join to combine smaller denominations into a larger one when the resulting value is exactly representable.
Frontend guidance
Do not treat join as dormant. It belongs in the active developer surface together with make_change, get_available_change_sns, and break.
Universal preamble (48 bytes)
Modern Change Service requests (make_change, break, join) frequently start their bodies with a 48-byte authenticated preamble. This structure identifies the coin being used for the operation and provides replay protection.