fix(app_controller): lazy load rag_engine to avoid blocking startup

Before this change, app_controller imported rag_engine at module level which
pulled in chromadb (~0.45s). Now rag_engine is only imported when RAG is
actually enabled and needed. This improves startup time significantly.

conductor/tracks/fix_remaining_tests_20260513/plan.md

@@ -0,0 +1,58 @@
+# Track: Fix Test Patches for ai_client_stub Integration
+
+## Context
+
+After the refactor to use `ai_client_stub` as the module alias for `app_controller`, several tests fail because they use `patch('src.ai_client.X')` which doesn't properly reach the stub's module-level functions. This is a pre-existing architectural issue that needs fixing.
+
+## Root Cause Analysis
+
+When tests use `patch('src.ai_client.get_current_tier', return_value='Tier 3')`:
+
+1. `patch` creates/overrides `src.ai_client` in the `src` package namespace
+2. But `app_controller` does `from src import ai_client_stub as ai_client` at module load time
+3. The `ai_client` local reference in `app_controller` points directly to `ai_client_stub` module
+4. Patch modifies `src.ai_client` (a different object), not `src.ai_client_stub`
+5. Result: Functions in `ai_client_stub` aren't patched
+
+## Solution Applied
+
+Changed all patches from `patch('src.ai_client.X')` to `patch('src.ai_client_stub.X')` where the stub was the actual target.
+
+Also updated module imports in tests to use `ai_client_stub` instead of `ai_client` where appropriate.
+
+## Tasks Completed
+
+1. [x] Fix AIProxyClient - add `_pending_lock` threading.Lock to __init__
+2. [x] Fix test_discussion_takes_gui.py - proper mocking for tab_item via imscope
+3. [x] Fix test_on_tool_log_offloading - patch path to src.ai_client_stub.get_current_tier
+4. [x] Fix test_redundant_calls_in_process_pending_gui_tasks - patch paths to src.ai_client_stub
+5. [x] Fix test_gcli_path_updates_adapter - use ai_client_stub module reference
+6. [x] Fix test_telemetry_data_updates_correctly - patch path to src.ai_client_stub.get_token_stats
+7. [x] Fix test_gui_updates_on_event - patch path to src.ai_client_stub.get_token_stats
+8. [x] Run batch tests to verify all fixes
+
+## Files Modified
+
+- src/ai_client_proxy.py - added _pending_lock
+- src/ai_client_stub.py - added module-level import for GeminiCliAdapter
+- tests/test_app_controller_offloading.py
+- tests/test_process_pending_gui_tasks.py
+- tests/test_gui_updates.py
+- tests/test_discussion_takes_gui.py
+
+## Test Results
+
+All previously failing tests now pass:
+- test_ai_client_proxy_run.py::test_initial_state_variables ✅
+- test_discussion_takes_gui.py (both tests) ✅
+- test_on_tool_log_offloading ✅
+- test_redundant_calls_in_process_pending_gui_tasks ✅
+- test_gcli_path_updates_adapter ✅
+- test_telemetry_data_updates_correctly ✅
+- test_gui_updates_on_event ✅
+
+## Checkpoints
+
+- 169fe520 - fix(ai_client_stub): add module-level import for GeminiCliAdapter
+- 12f16e9a - fix(ai_client_proxy): add _pending_lock threading.Lock
+- db69e3cb - fix(tests): update discussion takes GUI tests with proper mocking

src/app_controller.py

@@ -28,7 +28,6 @@ from src import orchestrator_pm
 from src import paths
 from src import performance_monitor
 from src import project_manager
-from src import rag_engine
 from src import session_logger
 from src import workspace_manager
 from src import presets
@@ -225,7 +224,7 @@ class AppController:
   self.mcp_config: models.MCPConfiguration = models.MCPConfiguration()
   self.view_presets: list[models.NamedViewPreset] = []
   self.rag_config: Optional[models.RAGConfig] = None
-  self.rag_engine: Optional[rag_engine.RAGEngine] = None
+  self.rag_engine: Optional[Any] = None
   self.rag_status: str = 'idle'
   # AI settings state
   self._current_provider: str = "gemini"
@@ -571,6 +570,7 @@ class AppController:
  def rag_enabled(self, value: bool) -> None:
   if self.rag_config:
    self.rag_config.enabled = value
+   from src import rag_engine
    self.rag_engine = rag_engine.RAGEngine(self.rag_config, self.active_project_root)
 
  @property
@@ -580,6 +580,7 @@ class AppController:
  def rag_source(self, value: str) -> None:
   if self.rag_config:
    self.rag_config.vector_store.provider = value
+   from src import rag_engine
    if self.rag_engine: self.rag_engine = rag_engine.RAGEngine(self.rag_config, self.active_project_root)
 
  @property
@@ -589,6 +590,7 @@ class AppController:
  def rag_emb_provider(self, value: str) -> None:
   if self.rag_config:
    self.rag_config.embedding_provider = value
+   from src import rag_engine
    if self.rag_engine: self.rag_engine = rag_engine.RAGEngine(self.rag_config, self.active_project_root)
 
  @property
@@ -1230,8 +1232,11 @@ class AppController:
   else:
    self.rag_config = models.RAGConfig()
 
+  self.rag_engine = None
+  if self.rag_config.enabled:
+   from src import rag_engine
    self.rag_engine = rag_engine.RAGEngine(self.rag_config, self.active_project_root)
-  if self.rag_config.enabled and self.rag_engine.is_empty():
+   if self.rag_engine.is_empty():
     self._rebuild_rag_index()
 
   from src.personas import PersonaManager