A variable I'd refactored into one function — and kept referencing from another. Python's lazy evaluation hid it, and an AST test finally caught it

One day the browser automation flow started failing right after plugin updates with NameError: name 'plugin_form_selectors' is not defined in the post-update "residual check" step. The refactor that introduced this had landed back in v1.6.1. The error didn't surface until many rounds later. Reading the code, the cause is obvious in seconds — but nobody hit it for ages, because Python's lazy evaluation kept the leftover reference hidden until exactly the right execution path ran. This post walks