Function primary_module_error 

fn primary_module_error(err: Error) -> TransactionSubmitError

Classifies a primary module’s failure to balance a transaction.

The module -> client trait boundary is still anyhow (#8821 part E narrows it), so this walks the error’s source() chain for the one condition callers must be able to act on: an InsufficientBalanceError means the primary module cannot fund the transaction, as opposed to a failure of the client, the database or the federation, which stays TransactionSubmitError::PrimaryModule.