Pause study when max responses limit is reached

studies/models.py

@@ -593,10 +593,27 @@ def has_reached_max_responses(self) -> bool:
     def check_and_pause_if_at_max_responses(self):
         """Check if max responses reached and pause the study if so.
 
-        Only pauses if the study is currently active.
+        Only pauses if the study is currently active. Uses the state machine's
+        pause trigger to properly transition and run callbacks.
         """
-        # TODO: Implement logic to pause study when max responses reached
-        pass
+        if self.max_responses is None:
+            return
+
+        if self.state != "active":
+            return
+
+        if not self.has_reached_max_responses:
+            return
+
+        # Refresh from DB to ensure the in-memory study is current before
+        # the pause transition triggers a save (via _finalize_state_change).
+        self.refresh_from_db()
+
+        # Use the state machine's pause trigger to properly transition
+        # and run callbacks (like notify_administrators_of_pause)
+        # Note: no explicit save() needed here because the state machine's
+        # _finalize_state_change callback already saves the model.
+        self.pause()  # No user since this is system-triggered
 
     @property
     def consent_videos(self):
@@ -825,12 +842,16 @@ def notify_administrators_of_activation(self, ev):
         )
 
     def notify_administrators_of_pause(self, ev):
+        user = ev.kwargs.get("user")
+        caller_name = (
+            user.get_short_name() if user else "System (max responses reached)"
+        )
         context = {
             "lab_name": self.lab.name,
             "study_name": self.name,
             "study_id": self.pk,
             "study_uuid": str(self.uuid),
-            "researcher_name": ev.kwargs.get("user").get_short_name(),
+            "researcher_name": caller_name,
             "action": ev.transition.dest,
         }
         send_mail.delay(
@@ -998,6 +1019,12 @@ def check_modification_of_approved_study(
         ):
             continue  # Skip, since the actual JSON content is the same - only exact_text changing
         if new != current:
+            # For file fields (e.g. image), None and "" are equivalent empty
+            # values that can differ between in-memory defaults and DB-loaded
+            # values. Treat them as unchanged.
+            if hasattr(current, "name") and hasattr(new, "name"):
+                if (current.name or "") == (new.name or ""):
+                    continue
             important_fields_changed = True
             break