Add no_photodiode keyword [skip CI]

src/npc_sessions/sessions.py

@@ -655,6 +655,8 @@ def keywords(self) -> list[str]:
                 self.keywords.append("late_autorewards")
             elif self.is_task:
                 self.keywords.append("early_autorewards")
+            if self.is_task and not getattr(self, "is_photodiode"):
+                self.keywords.append("no_photodiode")
             for t in self.epoch_tags:
                 if t not in self.keywords:
                     self.keywords.append(t)
@@ -1986,6 +1988,19 @@ def is_templeton(self) -> bool:
             "Not enough information to tell if this is a Templeton session"
         )
 
+    @npc_io.cached_property
+    def is_photodiode(self) -> bool:
+        """Do frame times from sync use photodiode info for the task data?
+        
+        - in cases where diode signal is unreliable, we use vsync + constant
+          monitor lag to estimate frame times
+        """
+        if not self.is_task:
+            raise AttributeError(f"{self.id} is not a session with behavior task")
+        task_frame_times = next(v for k,v in self.stim_frame_times if self.task_stim_name in k)
+        return any(np.array_equal(task_frame_times, array) for array in self.sync_data.constant_lag_frame_display_time_blocks)
+
+
     # helper properties -------------------------------------------------------- #
 
     @npc_io.cached_property