A developer asks Claude Code to 'refactor the user authentication module to be more maintainable.' Which characteristic of this request makes plan mode the correct choice?
Answer: The requirement is ambiguous — 'more maintainable' could mean multiple different architectural approaches, each valid but different
The primary reason for plan mode here is requirement ambiguity: 'more maintainable' could mean extracting pure functions, adding dependency injection, splitting a large class, improving naming, or rewriting with a different pattern. Each interpretation produces different changes to different files. Without plan mode, Claude picks one interpretation and acts on it — possibly not the one the developer intended. Plan mode forces Claude to state its interpretation before touching code, allowing course correction before 20 files are modified. Sensitive data handling (A) is a security concern, not a plan mode trigger. Multi-file doesn't always require planning (B) — bulk replacements are straightforward. Claude Code doesn't always use plan mode for refactoring (D).