diff --git a/tests/test_system_prompt_exposure.py b/tests/test_system_prompt_exposure.py
new file mode 100644
index 0000000..b96432b
--- /dev/null
+++ b/tests/test_system_prompt_exposure.py
@@ -0,0 +1,115 @@
+import unittest
+from unittest.mock import MagicMock, patch
+import os
+import sys
+from pathlib import Path
+
+# Add src to sys.path if needed
+sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+
+from src import ai_client
+from src.app_controller import AppController
+from src import models
+
+class TestSystemPromptExposure(unittest.TestCase):
+
+ def setUp(self):
+  # Reset ai_client globals
+  ai_client.set_use_default_base_prompt(True)
+  ai_client.set_base_system_prompt("")
+  ai_client.set_custom_system_prompt("")
+
+ def test_ai_client_get_combined_respects_use_default(self):
+  # 1. Verify ai_client._get_combined_system_prompt() respects set_use_default_base_prompt()
+  
+  # Default is True, should return _SYSTEM_PROMPT
+  default_prompt = ai_client._get_combined_system_prompt()
+  self.assertIn("You are a helpful coding assistant", default_prompt)
+  
+  # Set to False, should return override (empty by default)
+  ai_client.set_use_default_base_prompt(False)
+  override_prompt = ai_client._get_combined_system_prompt()
+  self.assertEqual(override_prompt, "")
+  
+  # Set override and verify
+  ai_client.set_base_system_prompt("Custom Base")
+  override_prompt = ai_client._get_combined_system_prompt()
+  self.assertEqual(override_prompt, "Custom Base")
+
+ def test_ai_client_set_base_overrides_when_default_false(self):
+  # 2. Verify ai_client.set_base_system_prompt() correctly overrides the base when use_default is False.
+  ai_client.set_use_default_base_prompt(False)
+  ai_client.set_base_system_prompt("Overridden Prompt")
+  combined = ai_client._get_combined_system_prompt()
+  self.assertEqual(combined, "Overridden Prompt")
+  
+  # If we switch back to default, it should ignore the override
+  ai_client.set_use_default_base_prompt(True)
+  combined = ai_client._get_combined_system_prompt()
+  self.assertIn("You are a helpful coding assistant", combined)
+  self.assertNotIn("Overridden Prompt", combined)
+
+ @patch('src.models.load_config')
+ @patch('src.paths.get_full_path_info')
+ @patch('src.project_manager.load_project')
+ @patch('src.ai_client.set_tool_preset')
+ @patch('src.ai_client.set_bias_profile')
+ @patch('src.session_logger.reset_session')
+ def test_app_controller_init_state_loads_prompts(self, mock_reset, mock_bias, mock_preset, mock_load_project, mock_path_info, mock_load_config):
+  # 3. Verify AppController.init_state() correctly loads base_system_prompt and use_default_base_prompt from a mock config.
+  
+  mock_config = {
+   "ai": {
+    "base_system_prompt": "Config Base Prompt",
+    "use_default_base_prompt": False,
+    "provider": "gemini",
+    "model": "gemini-2.5-flash-lite"
+   },
+   "projects": {"paths": [], "active": ""},
+   "gui": {"show_windows": {}}
+  }
+  mock_load_config.return_value = mock_config
+  mock_path_info.return_value = {
+   'logs_dir': {'path': Path('logs')},
+   'scripts_dir': {'path': Path('scripts')}
+  }
+  mock_load_project.return_value = {}
+  
+  app = AppController()
+  # Mock the event queue to avoid thread errors
+  app.event_queue = MagicMock()
+  
+  app.init_state()
+  
+  self.assertEqual(app.ui_base_system_prompt, "Config Base Prompt")
+  self.assertEqual(app.ui_use_default_base_prompt, False)
+
+ def test_app_controller_flush_saves_prompts(self):
+  # 4. Verify AppController._flush_to_config() correctly saves these fields.
+  app = AppController()
+  app.config = {"ai": {}, "projects": {}, "gui": {}}
+  app.ui_base_system_prompt = "Flushed Prompt"
+  app.ui_use_default_base_prompt = True
+  app.ui_global_system_prompt = "Global Sys"
+  app.ui_global_preset_name = "Default"
+  app.project_paths = []
+  app.active_project_path = ""
+  
+  # Initialize missing attributes expected by _flush_to_config
+  app.ui_separate_task_dag = False
+  app.ui_separate_usage_analytics = False
+  app.ui_separate_tier1 = False
+  app.ui_separate_tier2 = False
+  app.ui_separate_tier3 = False
+  app.ui_separate_tier4 = False
+  
+  # Mock current_provider/model properties
+  with patch.object(AppController, 'current_provider', 'gemini'), \
+       patch.object(AppController, 'current_model', 'gemini-model'):
+   app._flush_to_config()
+  
+  self.assertEqual(app.config["ai"]["base_system_prompt"], "Flushed Prompt")
+  self.assertEqual(app.config["ai"]["use_default_base_prompt"], True)
+
+if __name__ == '__main__':
+ unittest.main()