API changelog

Each product was originally implemented with its own request handling. The paths converged over time but never exactly, so error envelopes, idempotent replay and the point at which the wallet was debited could differ in small ways between one product and the next. Those differences were invisible until an integration handled several products and had to account for each.

All product now compose the same engines. One pricing resolution, one wallet lock, one state machine, one error envelope. The practical effect is that behaviour learned against one product holds for the rest.

The variation endpoints exposed whichever shape the upstream provider happened to return, so a client integrating data plans and cable bouquets wrote two parsers for what is conceptually one list. Switching provider could also change the payload without the endpoint changing.

The catalogue endpoints return one provider independent shape keyed by product_code, which is the same identifier the corresponding purchase call takes. Provider differences are resolved before the response is built.

Funds are reserved before the provider is contacted, which is what stops concurrent purchases overdrawing a wallet. When a provider then fails, the amount is credited back.

That reversal previously edited the original entry, which left no record that the purchase had been attempted at all. It now appends its own entry. The balance is unchanged either way; the difference is that a disputed balance is answerable from the ledger rather than from inference.