What does the setting "If my engine fails" do?

It is in Settings from version 1.9.14 and applies to books with an AI engine chosen in Book details. "Continue with another engine" is the default and works as BookyAI always has: if your engine fails, the Gemini rotation (then Ollama) writes the chapter, so the book always finishes. "Stay on my engine" never switches: the same engine is tried again after a pause, a chapter that still fails is marked as failed, the book moves on, and the failed chapters get one more pass at the end. Anything still failed can be regenerated from the book page. Each chapter shows which model wrote it.