Enable REPL mode transforms:
- Wraps top-level inputs that appear to be object literals (inputs starting with '{' without trailing ';') in parentheses
- Hoists all declarations as var for REPL persistence across vm.runInContext calls
- Wraps last expression in { proto: null, value: expr } for result capture
- Wraps code in sync/async IIFE to avoid parentheses around object literals