diff --git a/src/app_controller.py b/src/app_controller.py
index f709d3b0..61f29c5a 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -1844,17 +1844,34 @@ class AppController:
    tasks = self._pending_gui_tasks[:]
    self._pending_gui_tasks.clear()
   for task in tasks:
-   try:
-    action = task.get("action") or task.get("type")
-    if action:
-     session_logger.log_api_hook("PROCESS_TASK", action, str(task))
-     if action in self._gui_task_handlers:
-      self._gui_task_handlers[action](self, task)
-   except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, RuntimeError) as e:
-    logging.getLogger(__name__).debug("GUI task execution failed: %s", e, extra={"source": "app_controller._process_pending_gui_tasks"})
-    print(f"Error executing GUI task ({task.get('action') or task.get('type')}): {e}")
+   result = self._execute_gui_task_result(task)
+   if not result.ok:
+    err = result.errors[0]
+    action = task.get('action') or task.get('type') or 'unknown'
+    self._last_request_errors.append((f"gui_task[{action}]", err))
+    print(f"Error executing GUI task ({action}): {err.message}")
     traceback.print_exc()
 
+ def _execute_gui_task_result(self, task: dict) -> "Result[None]":
+  """Phase 6 Group 6.6: per-task execution with Result propagation.
+  On failure: any handler exception -> ErrorInfo(original=e).
+  Caller (`_process_pending_gui_tasks`) appends to
+  `self._last_request_errors` for sub-track 4 GUI."""
+  try:
+   action = task.get("action") or task.get("type")
+   if action:
+    session_logger.log_api_hook("PROCESS_TASK", action, str(task))
+    if action in self._gui_task_handlers:
+     self._gui_task_handlers[action](self, task)
+   return OK
+  except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, RuntimeError) as e:
+   return Result(data=None, errors=[ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=str(e),
+    source=f"app_controller._execute_gui_task_result[{task.get('action') or task.get('type')}]",
+    original=e,
+   )])
+
  def _process_pending_history_adds(self) -> None:
   """
   Synchronizes pending history entries to the active discussion and project state.
@@ -2126,15 +2143,98 @@ class AppController:
     ]
     for p in paths_to_check:
      if p.exists():
-      try:
-       with open(p, "r", encoding="utf-8") as rf:
-        return rf.read()
-      except (OSError, IOError, UnicodeDecodeError) as e:
-       logging.getLogger(__name__).debug("ref file read failed for %s: %s", p, e, extra={"source": "app_controller.cb_load_prior_log._resolve_log_ref"})
-       return f"[ERROR READING REF: {ref_file}]"
+      result = self._read_ref_file_result(p)
+      if result.ok:
+       return result.data
+      self._last_request_errors.append((f"ref_file_read[{ref_file}]", result.errors[0]))
+      return f"[ERROR READING REF: {ref_file}]"
     return match.group(0)
    return re.sub(pattern, replace_ref, content)
 
+  def _read_ref_file_result(self, p: Path) -> "Result[str]":
+   """Phase 6 Group 6.7: read a [REF:...] file content.
+   On failure: OSError/IOError/UnicodeDecodeError -> ErrorInfo(original=e).
+   Caller (`_resolve_log_ref`) appends to `self._last_request_errors`."""
+   try:
+    with open(p, "r", encoding="utf-8") as rf:
+     return Result(data=rf.read())
+   except (OSError, IOError, UnicodeDecodeError) as e:
+    return Result(data="", errors=[ErrorInfo(
+     kind=ErrorKind.INTERNAL,
+     message=str(e),
+     source=f"app_controller._read_ref_file_result[{p.name}]",
+     original=e,
+    )])
+
+ def _flush_to_project_result(self, cleaned_proj: dict, path: str) -> "Result[None]":
+  """Phase 6 Group 6.7: flush to project file with Result propagation.
+  On failure: OSError/IOError/PermissionError/RuntimeError -> ErrorInfo(original=e).
+  Caller (`_flush_to_project`) appends to `self._last_request_errors`."""
+  try:
+   project_manager.save_project(cleaned_proj, path)
+   return OK
+  except (OSError, IOError, PermissionError, RuntimeError) as e:
+   return Result(data=None, errors=[ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=str(e),
+    source=f"app_controller._flush_to_project_result[{path}]",
+    original=e,
+   )])
+
+ def _deserialize_active_track_result(self, at_data: dict) -> "Result[Any]":
+  """Phase 6 Group 6.7: deserialize active_track with Result propagation.
+  On failure: TypeError/ValueError/KeyError/AttributeError -> ErrorInfo(original=e).
+  Caller (`_refresh_from_project`) appends to `self._last_request_errors`."""
+  try:
+   tickets = []
+   for t_data in at_data.get("tickets", []):
+    tickets.append(models.Ticket(**t_data))
+   track = models.Track(
+    id=at_data.get("id"),
+    description=at_data.get("description"),
+    tickets=tickets
+   )
+   return Result(data=track)
+  except (TypeError, ValueError, KeyError, AttributeError) as e:
+   return Result(data=None, errors=[ErrorInfo(
+    kind=ErrorKind.INVALID_INPUT,
+    message=str(e),
+    source="app_controller._deserialize_active_track_result",
+    original=e,
+   )])
+
+ def _serialize_tool_calls_result(self, tool_calls: list) -> "Result[str]":
+  """Phase 6 Group 6.7: json-serialize tool_calls with Result propagation.
+  On failure: TypeError/ValueError -> ErrorInfo(original=e).
+  Caller falls back to '[TOOL CALLS PRESENT]' marker."""
+  try:
+   tc_str = json.dumps(tool_calls, indent=1)
+   return Result(data=tc_str)
+  except (TypeError, ValueError) as e:
+   return Result(data="", errors=[ErrorInfo(
+    kind=ErrorKind.INVALID_INPUT,
+    message=str(e),
+    source="app_controller._serialize_tool_calls_result",
+    original=e,
+   )])
+
+ def _parse_token_history_first_ts_result(self, item: dict) -> "Result[float]":
+  """Phase 6 Group 6.7: parse the first token_history timestamp.
+  On failure: ValueError/TypeError/KeyError/IndexError -> ErrorInfo(original=e).
+  Caller falls back to time.time() and records the error."""
+  try:
+   import datetime as _dt
+   first_ts = item['time']
+   dt = _dt.datetime.strptime(first_ts, '%Y-%m-%dT%H:%M:%S')
+   return Result(data=dt.timestamp())
+  except (ValueError, TypeError, KeyError, IndexError) as e:
+   return Result(data=0.0, errors=[ErrorInfo(
+    kind=ErrorKind.INVALID_INPUT,
+    message=str(e),
+    source="app_controller._parse_token_history_first_ts_result",
+    original=e,
+   )])
+
   entries = []
   disc_entries = []
   paired_tools = {}
@@ -2223,14 +2323,15 @@ class AppController:
         tool_calls = payload.get("tool_calls", [])
         content = text
         if tool_calls:
-         try:
-          tc_str = json.dumps(tool_calls, indent=1)
+         tc_result = self._serialize_tool_calls_result(tool_calls)
+         if tc_result.ok:
+          tc_str = tc_result.data
           if content:
            content += f"\n\n[TOOL CALLS]\n{tc_str}"
           else:
            content = f"[TOOL CALLS]\n{tc_str}"
-         except (TypeError, ValueError) as e:
-          logging.getLogger(__name__).debug("tool_calls json serialization failed: %s", e, extra={"source": "app_controller.cb_load_prior_log.tool_calls"})
+         else:
+          self._last_request_errors.append(("tool_calls_json_serialize", tc_result.errors[0]))
           if content:
            content += f"\n\n[TOOL CALLS PRESENT]"
           else:
@@ -2266,14 +2367,12 @@ class AppController:
   self.mma_tier_usage = new_mma_usage
   self._token_history = new_token_history
   if new_token_history:
-   try:
-    import datetime
-    first_ts = new_token_history[0]['time']
-    dt = datetime.datetime.strptime(first_ts, '%Y-%m-%dT%H:%M:%S')
-    self._session_start_time = dt.timestamp()
-   except (ValueError, TypeError, KeyError, IndexError) as e:
-    logging.getLogger(__name__).debug("token_history first_ts parse failed: %s", e, extra={"source": "app_controller.cb_load_prior_log.token_history"})
+   result = self._parse_token_history_first_ts_result(new_token_history[0])
+   if result.ok:
+    self._session_start_time = result.data
+   else:
     self._session_start_time = time.time()
+    self._last_request_errors.append(("token_history_first_ts_parse", result.errors[0]))
   self.prior_session_entries = entries
   self.prior_disc_entries = disc_entries
   self.prior_tool_calls = final_tool_calls
@@ -2333,14 +2432,52 @@ class AppController:
 
   self.submit_io(run_manual_prune)
 
+ def _load_project_from_path_result(self, pp: str) -> "Result[Dict[str, Any]]":
+  """Phase 6 Group 6.7: load a project from a path with Result propagation.
+  On failure: OSError/IOError/ValueError/TypeError/KeyError/AttributeError/tomllib.TOMLDecodeError
+  -> ErrorInfo(original=e). Caller stores the error for sub-track 4 GUI."""
+  try:
+   data = project_manager.load_project(pp)
+   return Result(data=data)
+  except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, tomllib.TOMLDecodeError) as e:
+   return Result(data={}, errors=[ErrorInfo(
+    kind=ErrorKind.NOT_FOUND,
+    message=str(e),
+    source=f"app_controller._load_project_from_path_result[{pp}]",
+    original=e,
+   )])
+
+ def _save_fallback_project_result(self, fallback_path: str) -> "Result[None]":
+  """Phase 6 Group 6.7: save fallback project with Result propagation.
+  On failure: OSError/IOError/PermissionError/RuntimeError -> ErrorInfo(original=e).
+  The save is best-effort; the app continues even on failure
+  (active_project_path stays empty; next save will use a proper path).
+  Per post-completion patch cb68d86f: catches RuntimeError too
+  (test sandbox FR1 guard raises RuntimeError)."""
+  try:
+   project_manager.save_project(self.project, fallback_path)
+   self.active_project_path = fallback_path
+   if fallback_path not in self.project_paths:
+    self.project_paths.append(fallback_path)
+   return OK
+  except (OSError, IOError, PermissionError, RuntimeError) as e:
+   return Result(data=None, errors=[ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=str(e),
+    source=f"app_controller._save_fallback_project_result[{fallback_path}]",
+    original=e,
+   )])
+
  def _load_active_project(self) -> Result[None]:
   """Loads the active project configuration, with fallbacks."""
+  aggregated_errors: List[ErrorInfo] = []
   if self.active_project_path and Path(self.active_project_path).exists():
-   try:
-    self.project = project_manager.load_project(self.active_project_path)
-   except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, tomllib.TOMLDecodeError) as e:
-    logging.getLogger(__name__).debug("load_project failed: %s", e, extra={"source": "app_controller._load_active_project.primary"})
-    print(f"Failed to load project {self.active_project_path}: {e}")
+   result = self._load_project_from_path_result(self.active_project_path)
+   if result.ok:
+    self.project = result.data
+   else:
+    aggregated_errors.append(result.errors[0])
+    print(f"Failed to load project {self.active_project_path}: {result.errors[0].message}")
     self.project = project_manager.migrate_from_legacy_config(self.config)
     self.active_project_path = ""
   else:
@@ -2349,36 +2486,28 @@ class AppController:
   if not self.active_project_path:
    for pp in self.project_paths:
     if Path(pp).exists():
-     try:
-      self.project = project_manager.load_project(pp)
+     result = self._load_project_from_path_result(pp)
+     if result.ok:
+      self.project = result.data
       self.active_project_path = pp
       break
-     except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, tomllib.TOMLDecodeError) as e:
-      logging.getLogger(__name__).debug("load_project failed for %s: %s", pp, e, extra={"source": "app_controller._load_active_project.fallback_loop"})
-      continue
+     aggregated_errors.append(result.errors[0])
+     continue
   if not self.active_project_path:
    name = self.project.get("project", {}).get("name", "project")
    fallback_path = f"{name}.toml"
-   try:
-    project_manager.save_project(self.project, fallback_path)
-    self.active_project_path = fallback_path
-    if fallback_path not in self.project_paths:
-     self.project_paths.append(fallback_path)
-   except (OSError, IOError, PermissionError, RuntimeError) as e:
-    logging.getLogger(__name__).debug(
-     "Could not save fallback project to %s: %s", fallback_path, e,
-     extra={"source": "app_controller._load_active_project.fallback_save"},
-    )
-    # The save is best-effort; the app can still operate without persisting
-    # the empty fallback (e.g., when the test sandbox FR1 guard blocks
-    # writes to the project root via the sys.addaudithook RuntimeError).
-    # active_project_path stays empty; the next save will use a proper path.
+   save_result = self._save_fallback_project_result(fallback_path)
+   if not save_result.ok:
+    aggregated_errors.append(save_result.errors[0])
   self.preset_manager = presets.PresetManager(Path(self.active_project_path).parent if self.active_project_path else None)
   self.tool_preset_manager = tool_presets.ToolPresetManager(Path(self.active_project_path).parent if self.active_project_path else None)
   from src.personas import PersonaManager
   self.persona_manager = PersonaManager(Path(self.active_project_path).parent if self.active_project_path else None)
   self._refresh_from_project()
   self._configure_mcp_for_project()
+  if aggregated_errors:
+   return Result(data=None, errors=aggregated_errors)
+  return OK
 
  def inject_context(self, data: dict) -> None:
   """
@@ -2600,17 +2729,32 @@ class AppController:
  def _run_event_loop(self):
   """Internal loop runner."""
 
-  def queue_fallback() -> None:
+  def queue_fallback() -> "Result[None]":
    while True:
-    try:
-     if hasattr(self, '_process_pending_gui_tasks'):
-      self._process_pending_gui_tasks()
-     if hasattr(self, '_process_pending_history_adds'):
-      self._process_pending_history_adds()
-    except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, RuntimeError) as e:
-     logging.getLogger(__name__).debug("queue fallback task error: %s", e, extra={"source": "app_controller.queue_fallback"})
+    result = self._run_pending_tasks_once_result()
+    if not result.ok:
+     self._report_worker_error("queue_fallback", result)
     time.sleep(0.1)
   self.submit_io(queue_fallback)
+
+ def _run_pending_tasks_once_result(self) -> "Result[None]":
+  """Phase 6 Group 6.7 (bounded retry Pattern 5 drain): single iteration of
+  the queue-fallback loop. On failure: any handler exception -> ErrorInfo.
+  Caller (`queue_fallback`) reports via _report_worker_error; the bounded
+  retry loop IS the Pattern 5 drain."""
+  try:
+   if hasattr(self, '_process_pending_gui_tasks'):
+    self._process_pending_gui_tasks()
+   if hasattr(self, '_process_pending_history_adds'):
+    self._process_pending_history_adds()
+   return OK
+  except (OSError, IOError, ValueError, TypeError, KeyError, AttributeError, RuntimeError) as e:
+   return Result(data=None, errors=[ErrorInfo(
+    kind=ErrorKind.INTERNAL,
+    message=str(e),
+    source="app_controller._run_pending_tasks_once_result",
+    original=e,
+   )])
   self._process_event_queue()
 
  @property
@@ -2824,13 +2968,9 @@ class AppController:
 
   cleaned_proj = project_manager.clean_nones(proj)
   if self.active_project_path:
-   try:
-    project_manager.save_project(cleaned_proj, self.active_project_path)
-   except (OSError, IOError, PermissionError, RuntimeError) as e:
-    logging.getLogger(__name__).debug(
-     "Could not save project to %s: %s", self.active_project_path, e,
-     extra={"source": "app_controller._flush_to_project"},
-    )
+   result = self._flush_to_project_result(cleaned_proj, self.active_project_path)
+   if not result.ok:
+    self._last_request_errors.append(("flush_to_project", result.errors[0]))
   else:
    logging.getLogger(__name__).debug(
     "Skipping _flush_to_project: active_project_path is empty.",
@@ -3124,19 +3264,14 @@ class AppController:
     self.mma_tier_usage[tier]["tool_preset"] = data.get("tool_preset", self.mma_tier_usage[tier].get("tool_preset"))
   at_data = mma_sec.get("active_track")
   if at_data:
-   try:
-    tickets = []
-    for t_data in at_data.get("tickets", []):
-     tickets.append(models.Ticket(**t_data))
-    self.active_track = models.Track(
-     id=at_data.get("id"),
-     description=at_data.get("description"),
-     tickets=tickets
-    )
+   result = self._deserialize_active_track_result(at_data)
+   if result.ok:
+    self.active_track = result.data
     self.active_tickets = at_data.get("tickets", []) # Keep dicts for UI table
-   except (TypeError, ValueError, KeyError, AttributeError) as e:
-    logging.getLogger(__name__).debug("active track deserialize failed: %s", e, extra={"source": "app_controller._refresh_from_project.active_track"})
-    print(f"Failed to deserialize active track: {e}")
+   else:
+    err = result.errors[0]
+    self._last_request_errors.append(("active_track_deserialize", err))
+    print(f"Failed to deserialize active track: {err.message}")
     self.active_track = None
   else:
    self.active_track = None