feat: add List.get support to JS backend

List.get(list, index) now correctly compiles to JavaScript, returning
Lux.Some(value) for valid indices and Lux.None() for out-of-bounds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/codegen/js_backend.rs

@@ -1917,6 +1917,14 @@ impl JsBackend {
                 let func = self.emit_expr(&args[1])?;
                 Ok(format!("({}.forEach({}), undefined)", list, func))
             }
+            "get" => {
+                let list = self.emit_expr(&args[0])?;
+                let idx = self.emit_expr(&args[1])?;
+                Ok(format!(
+                    "((__i, __l) => (__i >= 0 && __i < __l.length) ? Lux.Some(__l[__i]) : Lux.None())({}, {})",
+                    idx, list
+                ))
+            }
             _ => Err(JsGenError {
                 message: format!("Unknown List operation: {}", operation),
                 span: None,

src/main.rs

@@ -4263,6 +4263,29 @@ c")"#;
         assert!(js.contains("main_lux"), "main should be mangled: {}", js);
     }
 
+    #[test]
+    fn test_list_get_js_codegen() {
+        use crate::codegen::js_backend::JsBackend;
+        use crate::parser::Parser;
+        use crate::lexer::Lexer;
+
+        let source = r#"
+            fn main(): Unit = {
+                let xs = [10, 20, 30]
+                let result = List.get(xs, 1)
+                ()
+            }
+        "#;
+
+        let tokens = Lexer::new(source).tokenize().unwrap();
+        let program = Parser::new(tokens).parse_program().unwrap();
+        let mut backend = JsBackend::new();
+        let js = backend.generate(&program).unwrap();
+
+        assert!(js.contains("Lux.Some"), "JS should contain Lux.Some for List.get: {}", js);
+        assert!(js.contains("Lux.None"), "JS should contain Lux.None for List.get: {}", js);
+    }
+
     #[test]
     fn test_invalid_escape_sequence() {
         let result = eval(r#"let x = "\z""#);