Opt-in non-strict compatibility

Date: 2026-05-15 Area: engine Pull Request: #645

Added opt-in ES non-strict compatibility via --compat-non-strict-mode / "compat-non-strict-mode" for arguments objects, with statement execution, and legacy delete return values in both interpreter and bytecode modes. When enabled, ordinary functions, methods, accessors, and generators receive an unmapped arguments object while arrows keep lexical lookup; arguments stays an ordinary identifier that can be shadowed. with uses object environment lookup with Symbol.unscopables, identifier calls preserve the object as this, bytecode captures hidden with-object locals so closures created inside with keep resolving correctly, and delete returns false for non-deletable bindings/properties instead of throwing. language.md. language.md. language.md. interpreter.md. bytecode-vm.md.