Class DuplicatePolicyError

Thrown when creating a Policy that clashes with one already on the account. The backend permits only one policy per type + chain, and returns a 400 with a "Duplicate policy type" message when that constraint is violated; the SDK surfaces that as this typed error.

This is a subclass of ApiError (with status === 400), so existing catch (e) { if (e instanceof ApiError) ... } handlers continue to work; callers wanting to special-case the duplicate can check for DuplicatePolicyError specifically.