Builds a failed ChatResult (success: false). By default the shape
mirrors BaseLLM's own error construction: empty choices, zero usage,
statusText: 'error'. errorInfo is only attached when supplied, so tests
can model both diagnosed and undiagnosed failures.
Builds a failed ChatResult (
success: false). By default the shape mirrors BaseLLM's own error construction: empty choices, zero usage,statusText: 'error'.errorInfois only attached when supplied, so tests can model both diagnosed and undiagnosed failures.