test: fix external editor test to use real temp file that exists

tests/test_external_editor_gui.py

@@ -61,8 +61,14 @@ def test_vscode_launches_with_diff_view(live_gui):
     print(f"\n=== VSCODE LAUNCH TEST ===")
     print(f"VSCode before:\n{before if before.strip() else 'not running'}")
 
-    sample_patch = """--- a/test.py
-+++ b/test.py
+    with tempfile.NamedTemporaryFile(mode='w', suffix='.py', delete=False, encoding='utf-8') as f:
+        f.write('HELLO_WORLD = "original"\n')
+        f.write('def main():\n')
+        f.write('    pass\n')
+        test_file = f.name
+
+    sample_patch = f"""--- a/{Path(test_file).name}
++++ b/{Path(test_file).name}
 @@ -1,2 +1,3 @@
  HELLO_WORLD = "original"
 -HELLO_WORLD = "modified"
@@ -73,7 +79,7 @@ def test_vscode_launches_with_diff_view(live_gui):
 
     client.push_event("show_patch_modal", {
         "patch_text": sample_patch,
-        "file_paths": ["test.py"]
+        "file_paths": [test_file]
     })
 
     time.sleep(2)
@@ -99,6 +105,8 @@ def test_vscode_launches_with_diff_view(live_gui):
     client.push_event("hide_patch_modal", {})
     time.sleep(1)
 
+    os.unlink(test_file)
+
 
 @pytest.mark.integration
 @pytest.mark.timeout(30)