Add strip_fences option and fix exec() scoping for nested functions

- Add strip_fences field to PromptStep for removing markdown code fences
- Fix exec() to use same dict for globals and locals, allowing nested
  functions to access module-level imports
- Add GUI checkbox for strip_fences option
- Update CLAUDE.md with improved documentation

Co-Authored-By: Claude Opus 4.5 <[email protected]>

tests/test_runner.py

@@ -296,6 +296,54 @@ class TestExecuteCodeStep:
         assert success is True
         assert outputs2["total"] == 15
 
+    def test_nested_function_can_access_imports(self):
+        """Nested functions should be able to access module-level imports.
+
+        This tests a fix for a scoping bug where exec() with separate
+        globals/locals dicts caused nested functions to fail when accessing
+        imported modules. The fix uses the same dict for both globals and
+        locals so imports are visible to nested function closures.
+        """
+        step = CodeStep(
+            code="""
+import re
+
+def parse_numbers(text):
+    # This should be able to access 're' from the outer scope
+    matches = re.findall(r'\\d+', text)
+    return [int(m) for m in matches]
+
+result = parse_numbers(input)
+""",
+            output_var="result"
+        )
+        variables = {"input": "abc 123 def 456 ghi"}
+
+        outputs, success = execute_code_step(step, variables)
+
+        assert success is True
+        assert outputs["result"] == [123, 456]
+
+    def test_nested_function_can_access_outer_variables(self):
+        """Nested functions should access variables defined in outer scope."""
+        step = CodeStep(
+            code="""
+multiplier = 10
+
+def multiply_all(numbers):
+    return [n * multiplier for n in numbers]
+
+result = multiply_all([1, 2, 3])
+""",
+            output_var="result"
+        )
+        variables = {"input": ""}
+
+        outputs, success = execute_code_step(step, variables)
+
+        assert success is True
+        assert outputs["result"] == [10, 20, 30]
+
 
 class TestRunTool:
     """Tests for run_tool function."""