diff --git a/src/app_controller.py b/src/app_controller.py
index bc6ec06d..b571811c 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -1326,18 +1326,19 @@ class AppController:
 
  def startup_timeline(self) -> dict:
   """Returns a dict with all startup timestamps and precomputed deltas. Fields: init_start_ts, appcontroller_init_done_ts, gui_run_started_ts, warmup_done_ts, first_frame_ts, warmup_ms, appcontroller_init_ms, gui_setup_ms, first_render_ms, first_frame_after_init_ms, first_frame_after_warmup_ms. The 3 phase breakdowns answer 'which main-thread phase dominated?': AppController init, GUI bundle setup, first render. [SDM: src/app_controller.py:startup_timeline] [C: src/api_hooks.py:HookHandler.do_GET /api/startup_timeline]"""
+  cold_start = self.cold_start_ts
   result: dict = {
-   "cold_start_ts":              self.cold_start_ts,
+   "cold_start_ts":              cold_start.data if cold_start.ok else None,
    "init_start_ts":              self._init_start_ts,
    "appcontroller_init_done_ts": self._appcontroller_init_done_ts,
    "gui_run_started_ts":         self._gui_run_started_ts,
    "warmup_done_ts":             self._warmup_done_ts,
    "first_frame_ts":             self._first_frame_ts,
   }
-  if self.cold_start_ts is not None:
-   result["module_imports_ms"] = (self._init_start_ts - self.cold_start_ts) * 1000
+  if cold_start.ok:
+   result["module_imports_ms"] = (self._init_start_ts - cold_start.data) * 1000
    if self._first_frame_ts is not None:
-    result["cold_start_to_first_frame_ms"] = (self._first_frame_ts - self.cold_start_ts) * 1000
+    result["cold_start_to_first_frame_ms"] = (self._first_frame_ts - cold_start.data) * 1000
   else:
    result["module_imports_ms"] = None
   if self._warmup_done_ts is not None: 
@@ -1372,13 +1373,25 @@ class AppController:
  def cold_start_ts(self) -> "Optional[float]":
   """Timestamp captured at the very first line of sloppy.py (the entry
   point). Used to compute the full 'Python start to first frame' latency,
-  which is dominated by module imports. None if the entry point didn't
-  expose _SLOPPY_COLD_START_TS. [SDM: src/app_controller.py:cold_start_ts]"""
+  which is dominated by module imports. Returns Result with errors if the
+  entry point didn't expose _SLOPPY_COLD_START_TS. [SDM: src/app_controller.py:cold_start_ts]"""
   try:
    import sloppy as _sloppy
-   return getattr(_sloppy, "_SLOPPY_COLD_START_TS", None)
-  except (ImportError, AttributeError):
-   return None
+   ts = getattr(_sloppy, "_SLOPPY_COLD_START_TS", None)
+   if ts is None:
+    return Result(data=0.0, errors=[ErrorInfo(
+     kind=ErrorKind.NOT_READY,
+     message="cold start timestamp not exposed by sloppy entry point",
+     source="app_controller.cold_start_ts",
+    )])
+   return Result(data=float(ts))
+  except (ImportError, AttributeError) as e:
+   return Result(data=0.0, errors=[ErrorInfo(
+    kind=ErrorKind.NOT_READY,
+    message=str(e),
+    source="app_controller.cold_start_ts",
+    original=e,
+   )])
 
  def _on_warmup_complete_for_timeline(self, snap: dict) -> None:
   """Callback registered with the WarmupManager. Stamps warmup_done_ts and logs the timeline to stderr. [C: src/app_controller.py:startup_timeline]"""