Apps Script's V8 Migration Trap: One Rhino Pattern Breaks Everything

Apps Script's V8 runtime introduces a parse-time failure model that differs fundamentally from Rhino: any Rhino-specific syntax anywhere in your project—including forgotten utility files—prevents the entire application from initializing, not individual functions. This all-or-nothing behavior requires comprehensive audits to identify and fix deprecated patterns like for each loops, XML literals, and prototype methods before enabling V8, making it far more complex than the simple one-line configuration change suggests.