diff --git a/rlm/environments/local_repl.py b/rlm/environments/local_repl.py
index 5aa1b69..57301e4 100644
--- a/rlm/environments/local_repl.py
+++ b/rlm/environments/local_repl.py
@@ -1,6 +1,5 @@
 import copy
 import io
-import json
 import os
 import shutil
 import sys
@@ -250,22 +249,16 @@ def add_context(
 
         var_name = f"context_{context_index}"
 
+        # Store context directly in locals (with isolation for mutable types)
         if isinstance(context_payload, str):
-            context_path = os.path.join(self.temp_dir, f"context_{context_index}.txt")
-            with open(context_path, "w") as f:
-                f.write(context_payload)
-            self.execute_code(f"with open(r'{context_path}', 'r') as f:\n    {var_name} = f.read()")
+            self.locals[var_name] = context_payload
         else:
-            context_path = os.path.join(self.temp_dir, f"context_{context_index}.json")
-            with open(context_path, "w") as f:
-                json.dump(context_payload, f)
-            self.execute_code(
-                f"import json\nwith open(r'{context_path}', 'r') as f:\n    {var_name} = json.load(f)"
-            )
+            # Dicts/lists - deep copy for isolation as per SupportsPersistence protocol
+            self.locals[var_name] = copy.deepcopy(context_payload)
 
         # Alias context_0 as 'context' for backward compatibility
         if context_index == 0:
-            self.execute_code(f"context = {var_name}")
+            self.locals["context"] = self.locals[var_name]
 
         self._context_count = max(self._context_count, context_index + 1)
         return context_index
diff --git a/tests/test_local_repl_persistent.py b/tests/test_local_repl_persistent.py
index f654679..30ede83 100644
--- a/tests/test_local_repl_persistent.py
+++ b/tests/test_local_repl_persistent.py
@@ -63,6 +63,40 @@ def test_context_alias_points_to_first(self):
         assert repl.locals["is_first"] is True
         repl.cleanup()
 
+    def test_context_dict_is_copy(self):
+        """Test that dict context is a deep copy, not a reference."""
+        repl = LocalREPL()
+
+        context_dict = {"key": "original", "nested": {"inner": "value"}}
+        repl.add_context(context_dict)
+
+        # Modify the original after adding
+        context_dict["key"] = "modified"
+        context_dict["nested"]["inner"] = "modified_inner"
+
+        # Stored context should remain unchanged
+        assert repl.locals["context_0"]["key"] == "original"
+        assert repl.locals["context_0"]["nested"]["inner"] == "value"
+
+        repl.cleanup()
+
+    def test_context_list_is_copy(self):
+        """Test that list context is a deep copy, not a reference."""
+        repl = LocalREPL()
+
+        context_list = [{"item": "original"}, [1, 2, 3]]
+        repl.add_context(context_list)
+
+        # Modify the original after adding
+        context_list[0]["item"] = "modified"
+        context_list[1].append(4)
+
+        # Stored context should remain unchanged
+        assert repl.locals["context_0"][0]["item"] == "original"
+        assert repl.locals["context_0"][1] == [1, 2, 3]
+
+        repl.cleanup()
+
 
 class TestLocalREPLHistory:
     """Tests for message history storage in LocalREPL for persistent sessions."""