Expose structured generation errors to consumers

types.go

@@ -665,10 +665,10 @@ type StructuredOutputJSONSpec struct {
 // and retained copies. It is responsible for the cancellation behavior of any
 // work it starts and for synchronizing access to retained or shared data.
 //
-// A returned error makes Run or RunPrepared return ErrLLMGenerate while
-// preserving the client error through errors.Is. A nil response with a nil
-// error also produces ErrLLMGenerate. Promptkit copies the non-nil response
-// before returning from either method.
+// An arbitrary returned error makes Run or RunPrepared return ErrLLMGenerate
+// while preserving the client error through errors.Is rather than translating
+// it. A nil response with a nil error also produces ErrLLMGenerate. Promptkit
+// copies the non-nil response before returning from either method.
 type LLMClient interface {
 	Generate(context.Context, GenerateRequest) (*GenerateResponse, error)
 }