diff --git a/src/app_controller.py b/src/app_controller.py
index 4c8919a1..eccfd157 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -3497,7 +3497,7 @@ class AppController:
 
  def _rag_search_result(self, user_msg: str) -> "Result[list[Metadata]]":
   """Per-event handler (Phase 6 Group 6.6): RAG search via the engine.
-  Returns Result[List[Dict]]. On failure: any engine/SDK exception
+  Returns Result[List[RAGChunk]]. On failure: any engine/SDK exception
   -> ErrorInfo(original=e). Caller (`_handle_request_event`) appends
   to `self._last_request_errors` for sub-track 4 GUI display."""
   if not (self.rag_engine and self.rag_config and self.rag_config.enabled):
@@ -4411,7 +4411,7 @@ class AppController:
   if self.ui_auto_scroll_tool_calls:
    self._scroll_tool_calls_to_bottom = True
 
- def _confirm_and_run(self, script: str, base_dir: str, qa_callback: Optional[Callable[[str], str]] = None, patch_callback: Optional[Callable[[str, str], Result[str]]] = None) -> Optional[str]:
+ def _confirm_and_run(self, script: str, base_dir: str, qa_callback: Optional[Callable[[str], str]] = None, patch_callback: Optional[Callable[[str, str], Result[str]]] = None) -> str:
   """
     [C: tests/test_arch_boundary_phase2.py:TestArchBoundaryPhase2.test_mutating_tool_triggers_callback, tests/test_arch_boundary_phase2.py:TestArchBoundaryPhase2.test_rejection_prevents_dispatch]
   """
@@ -4444,7 +4444,7 @@ class AppController:
      del self._pending_actions[dialog._uid]
   if not approved:
    self._append_tool_log(final_script, "REJECTED by user")
-   return None
+   return ""
   self.ai_status = "running powershell..."
   output = shell_runner.run_powershell(final_script, base_dir, qa_callback=qa_callback, patch_callback=patch_callback)
   self._append_tool_log(final_script, output)
diff --git a/src/command_palette.py b/src/command_palette.py
index 8efe7d91..1b124b50 100644
--- a/src/command_palette.py
+++ b/src/command_palette.py
@@ -47,8 +47,8 @@ class CommandRegistry:
  def all(self) -> List[Command]:
   return list(self._commands.values())
 
- def get(self, command_id: str) -> Optional[Command]:
-  return self._commands.get(command_id)
+ def get(self, command_id: str) -> Command:
+  return self._commands.get(command_id) or Command(id="", title="", category="uncategorized", action=lambda: None)
 
 
 def fuzzy_match(query: str, candidates: List[Command], top_n: int = 20) -> List[ScoredCommand]:
diff --git a/src/diff_viewer.py b/src/diff_viewer.py
index b4bfa0b3..311452da 100644
--- a/src/diff_viewer.py
+++ b/src/diff_viewer.py
@@ -114,14 +114,14 @@ def parse_diff(diff_text: str) -> List[DiffFile]:
  
  return files
 
-def get_line_color(line: str) -> Optional[str]:
+def get_line_color(line: str) -> str:
  """
  [C: tests/test_diff_viewer.py:test_get_line_color]
  """
  if   line.startswith("+"):  return "green"
  elif line.startswith("-"):  return "red"
  elif line.startswith("@@"): return "cyan"
- return None
+ return ""
 
 def apply_patch_to_file(patch_text: str, base_dir: str = ".") -> Tuple[bool, str]:
  """
diff --git a/src/fuzzy_anchor.py b/src/fuzzy_anchor.py
index 938640fe..219608fa 100644
--- a/src/fuzzy_anchor.py
+++ b/src/fuzzy_anchor.py
@@ -37,7 +37,9 @@ class FuzzyAnchor:
   }
 
  @classmethod
- def resolve_slice(cls, text: str, slice_data: dict) -> Optional[Tuple[int, int]]:
+ def resolve_slice(cls, text: str, slice_data: dict) -> Tuple[int, int]:
+  """Returns (start_line, end_line) on success, or (-1, -1) if unresolved."""
+  result: Tuple[int, int] = (-1, -1)
   """
   [C: tests/test_fuzzy_anchor.py:TestFuzzyAnchor.test_resolve_slice_anchor_mismatch_returns_none, tests/test_fuzzy_anchor.py:TestFuzzyAnchor.test_resolve_slice_exact_match, tests/test_fuzzy_anchor.py:TestFuzzyAnchor.test_resolve_slice_line_deleted_before_returns_none, tests/test_fuzzy_anchor.py:TestFuzzyAnchor.test_resolve_slice_line_inserted_before, tests/test_fuzzy_anchor.py:TestFuzzyAnchor.test_resolve_slice_multiple_lines_changed]
   """
@@ -54,7 +56,7 @@ class FuzzyAnchor:
   # 2. Fuzzy match
   start_ctx = slice_data["start_context"]
   end_ctx   = slice_data["end_context"]
-  if not start_ctx or not end_ctx: return None
+  if not start_ctx or not end_ctx: return (-1, -1)
 
   # Search for start_ctx
   best_s = -1
@@ -68,7 +70,7 @@ class FuzzyAnchor:
     best_s = i
     break
   
-  if best_s == -1: return None
+  if best_s == -1: return (-1, -1)
 
   # Search for end_ctx after start_ctx
   best_e = -1
@@ -87,4 +89,4 @@ class FuzzyAnchor:
   if best_e != -1:
    return (best_s + 1, best_e)
   
-  return None
+  return (-1, -1)
diff --git a/src/multi_agent_conductor.py b/src/multi_agent_conductor.py
index 9ed0597c..b94211f8 100644
--- a/src/multi_agent_conductor.py
+++ b/src/multi_agent_conductor.py
@@ -61,7 +61,7 @@ class WorkerPool:
   self._lock = threading.Lock()
   self._semaphore = threading.Semaphore(max_workers)
 
- def spawn(self, ticket_id: str, target: Callable, args: tuple) -> Optional[threading.Thread]:
+ def spawn(self, ticket_id: str, target: Callable, args: tuple) -> threading.Thread:
   """
   Spawns a new worker thread if the pool is not full.
   Returns the thread object or None if full.
@@ -69,7 +69,7 @@ class WorkerPool:
   """
   with self._lock:
    if len(self._active) >= self.max_workers:
-    return None
+    return threading.Thread()  # sentinel: empty thread, not started
   
   def wrapper(*a, **kw):
    try:
diff --git a/src/patch_modal.py b/src/patch_modal.py
index feb6daa0..f995957a 100644
--- a/src/patch_modal.py
+++ b/src/patch_modal.py
@@ -4,14 +4,16 @@ from typing      import Optional, Callable, List
 
 @dataclass
 class PendingPatch:
- patch_text: str
- file_paths: List[str]
- generated_by: str
- timestamp: float
+ patch_text:   str = ""
+ file_paths:   List[str] = field(default_factory=list)
+ generated_by: str = ""
+ timestamp:    float = 0.0
+
+EMPTY_PATCH: PendingPatch = PendingPatch()
 
 class PatchModalManager:
  def __init__(self):
-  self._pending_patch: Optional[PendingPatch] = None
+  self._pending_patch: PendingPatch = EMPTY_PATCH
   self._show_modal: bool = False
   self._on_apply_callback: Optional[Callable[[str], bool]] = None
   self._on_reject_callback: Optional[Callable[[], None]] = None
@@ -30,7 +32,7 @@ class PatchModalManager:
   self._show_modal = True
   return True
   
- def get_pending_patch(self) -> Optional[PendingPatch]:
+ def get_pending_patch(self) -> "PendingPatch":
   """
     [C: tests/test_patch_modal.py:test_patch_modal_manager_init, tests/test_patch_modal.py:test_reject_patch, tests/test_patch_modal.py:test_request_patch_approval, tests/test_patch_modal.py:test_reset]
   """
@@ -66,7 +68,7 @@ class PatchModalManager:
   """
     [C: tests/test_patch_modal.py:test_reject_callback, tests/test_patch_modal.py:test_reject_patch]
   """
-  self._pending_patch = None
+  self._pending_patch = EMPTY_PATCH
   self._show_modal = False
   if self._on_reject_callback:
    self._on_reject_callback()
@@ -81,7 +83,7 @@ class PatchModalManager:
   """
     [C: tests/test_patch_modal.py:test_reset]
   """
-  self._pending_patch = None
+  self._pending_patch = EMPTY_PATCH
   self._show_modal = False
   self._on_apply_callback = None
   self._on_reject_callback = None
diff --git a/tests/test_diff_viewer.py b/tests/test_diff_viewer.py
index d788401b..3be120d2 100644
--- a/tests/test_diff_viewer.py
+++ b/tests/test_diff_viewer.py
@@ -92,7 +92,7 @@ def test_get_line_color() -> None:
  assert get_line_color("+added") == "green"
  assert get_line_color("-removed") == "red"
  assert get_line_color("@@ -1,3 +1,4 @@") == "cyan"
- assert get_line_color(" context") == None
+ assert get_line_color(" context") == ""
 
 def test_apply_patch_simple() -> None:
  with tempfile.TemporaryDirectory() as tmpdir:
diff --git a/tests/test_fuzzy_anchor.py b/tests/test_fuzzy_anchor.py
index 1ca8b809..37feb1ff 100644
--- a/tests/test_fuzzy_anchor.py
+++ b/tests/test_fuzzy_anchor.py
@@ -39,7 +39,7 @@ class TestFuzzyAnchor:
   modified = "line0\nline2\nline3\nline4\n"
   slc = FuzzyAnchor.create_slice(original, 2, 4)
   result = FuzzyAnchor.resolve_slice(modified, slc)
-  assert result is None
+  assert result == (-1, -1)
 
  def test_resolve_slice_multiple_lines_changed(self):
   original = "line0\nline1\nline2\nline3\nline4\n"
@@ -56,4 +56,4 @@ class TestFuzzyAnchor:
   modified = "foo\nbar\nbaz\ndelta\nepsilon\n"
   slc = FuzzyAnchor.create_slice(original, 2, 3)
   result = FuzzyAnchor.resolve_slice(modified, slc)
-  assert result is None
+  assert result == (-1, -1)
diff --git a/tests/test_parallel_execution.py b/tests/test_parallel_execution.py
index 9a9683b8..44408f9f 100644
--- a/tests/test_parallel_execution.py
+++ b/tests/test_parallel_execution.py
@@ -28,7 +28,7 @@ def test_worker_pool_limit():
 
  # Try to spawn a 3rd task
  t3 = pool.spawn("t3", slow_task, (event3,))
- assert t3 is None
+ assert not t3.is_alive()
  assert pool.get_active_count() == 2
 
  # Wait for tasks to finish
diff --git a/tests/test_patch_modal.py b/tests/test_patch_modal.py
index 03737e0e..c6995914 100644
--- a/tests/test_patch_modal.py
+++ b/tests/test_patch_modal.py
@@ -6,7 +6,7 @@ from src.patch_modal import (
 
 def test_patch_modal_manager_init():
   manager = PatchModalManager()
-  assert manager.get_pending_patch() is None
+  assert manager.get_pending_patch().patch_text == ""
   assert manager.is_modal_shown() is False
 
 def test_request_patch_approval():
@@ -28,7 +28,7 @@ def test_reject_patch():
   manager.request_patch_approval("diff", ["file.py"])
   
   manager.reject_patch()
-  assert manager.get_pending_patch() is None
+  assert manager.get_pending_patch().patch_text == ""
   assert manager.is_modal_shown() is False
 
 def test_close_modal():
@@ -75,7 +75,7 @@ def test_reset():
   
   manager.reset()
   
-  assert manager.get_pending_patch() is None
+  assert manager.get_pending_patch().patch_text == ""
   assert manager.is_modal_shown() is False
 
 def test_get_patch_modal_manager_singleton():