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Reports whether an error from the pre-generated wallet API is a server-side (5xx) failure — the only case where we fall back to the on-device binary DKG flow, since a 5xx is transient and safe to retry. Every other failure (4xx client errors such as the enclave "wallet already exists" rejection, auth failures, transport/IO errors, and share decode/validation failures) is surfaced immediately, because a binary retry would not resolve it and would only add a full DKG round of latency.