refactor: address review feedback

src/puyapy/awst_build/eb/arc4/_base.py

@@ -138,6 +138,9 @@ class _ARC4ArrayExpressionBuilder(BytesBackedInstanceExpressionBuilder[pytypes.A
     @typing.override
     def iterate(self) -> Expression:
         if not self.pytype.items.wtype.immutable:
+            # this case is an error raised during AWST validation
+            # adding a front end specific message here to compliment the error message
+            # raise across all front ends
             logger.info(
                 "use `algopy.urange(<array>.length)` to iterate by index",
                 location=self.source_location,

src/puyapy/awst_build/eb/arc4/string.py

@@ -103,10 +103,13 @@ def augmented_assignment(
         else:
             value = expect.argument_of_type_else_dummy(rhs, self.pytype).resolve()
 
+        # TODO: does this actually need to be a AugmentedAssignment node to ensure LHS is only
+        #       evaluated once
+        lhs = self.single_eval().resolve_lvalue()
         return AssignmentStatement(
-            target=self.resolve_lvalue(),
+            target=lhs,
             value=ArrayConcat(
-                left=self.resolve(),
+                left=lhs,
                 right=value,
                 wtype=wtypes.arc4_string_alias,
                 source_location=location,