feat(child): auto create parent-child conversations

mini-program/app/service/im.py

@@ -217,6 +217,28 @@ def create_parent_child_message(
     )
 
 
+def ensure_parent_child_conversation(
+    db: Session,
+    *,
+    parent_user_id: int,
+    child_id: int,
+) -> int:
+    child_row = assert_parent_child_access(db, user_id=parent_user_id, child_id=child_id)
+    parent_row = _get_parent_row(db, parent_user_id)
+    if not parent_row:
+        raise HTTPException(status_code=404, detail="parent not found")
+
+    return _get_or_create_conversation(
+        db=db,
+        conversation_type=PARENT_CHILD_CONVERSATION_TYPE,
+        participant_a_type=CHILD_PARTICIPANT_TYPE,
+        participant_a_id=str(child_id),
+        participant_b_type=PARENT_PARTICIPANT_TYPE,
+        participant_b_id=str(parent_user_id),
+        pair_key=f"{child_id}:{parent_user_id}",
+    )
+
+
 def create_device_message(
     db: Session,
     *,