sbi swaps three network-spec routes for typed configs, so bad settings fail where you write them

A dropped keyword is the kind of bug that lets the job finish. The old factory functions accepted any keyword handed to them, because their signature was the union of every setting any model in the family might want, and anything the chosen model did not use was discarded on the way to the network ^[6][7]. Training completes, the log looks like the script, and what comes back is a network that differs from the one written down. The only symptom is a posterior that is worse than it should be, which is indistinguishable from a hard inference problem.

Splitting that union into one frozen dataclass per model moves the check to the line where the setting is typed ^[3][9]. The report lists three ways of being wrong, all of which now raise before training: an unknown field name, a bad value for a known field, and a setting that belongs to a sibling model rather than this one ^[10]. Two of those are the constructor refusing an argument it has no slot for, and one is validation of the value itself ^[21]. None of them require a GPU to discover.

The most instructive engineering in the write-up is a removal. The first design had `build()` take a `BuildContext` object carrying shape, device and z-scoring statistics; the contributor reports that mentor Jan Teusen noticed the parameter was never read, since everything in it could be derived from the training batch already being passed, so it was cut as a premature abstraction ^[16]. That abstraction was killed by implementing it rather than by arguing about it, which is the cheaper of the two ways to find out.

The NLE extension is where the naming stopped being cosmetic. NPE models parameters given data and NLE models data given parameters, so the same builder serves opposite roles, and a signature reading `build(batch_theta, batch_x)` is correct for one family and backwards for the other ^[17]. Backwards here means the standardization lands on the wrong variable, which trains without complaint. The fix was to name the arguments by role, `build(batch_input, batch_condition)`, and leave the trainer to decide which is which so the config never has to know ^[18].

One caveat on provenance: this is the contributor's own final work product post for the project, mentored by Jan Teusen and Nicholas Junge under NumFOCUS and the sbi-dev/sbi sub-organisation ^[19], and it quantifies neither how much downstream code the deprecation warning touches nor when the string route stops working ^[11]. The claim being made is narrow and checkable, though. Configuration that the model cannot honour used to reach the network and vanish; now it does not compile past the constructor.