When enterprise API returns 403/404, the response contains error JSON
instead of expected data structure. Code was accessing fields directly
causing KeyError → 500 Internal Server Error.
Changes:
- Add enterprise-specific error classes (EnterpriseAPIError, etc.)
- Implement centralized error validation in EnterpriseRequest.send_request()
- Extract error messages from API responses (message/error/detail fields)
- Raise domain-specific errors based on HTTP status codes
- Preserve backward compatibility with raise_for_status parameter
This prevents KeyError crashes and returns proper HTTP error codes
(403/404) instead of 500 errors.
