Ensure msgs are sent in right order, fix echo bug

bug: only one local echo message delegate could be seen because all
echo eventId were the same

src/python/matrix_client.py

@@ -7,7 +7,8 @@ import platform
 from contextlib import suppress
 from datetime import datetime
 from types import ModuleType
-from typing import Dict, Optional, Type
+from typing import DefaultDict, Dict, Optional, Type
+from uuid import uuid4
 
 import nio
 from nio.rooms import MatrixRoom
@@ -31,6 +32,9 @@ class MatrixClient(nio.AsyncClient):
 
         self.sync_task: Optional[asyncio.Future] = None
 
+        self.send_locks: DefaultDict[str, asyncio.Lock] = \
+                DefaultDict(asyncio.Lock)  # {room_id: lock}
+
         super().__init__(homeserver=homeserver, user=user, device_id=device_id)
 
         self.connect_callbacks()
@@ -131,14 +135,15 @@ class MatrixClient(nio.AsyncClient):
         TimelineMessageReceived(
             event_type    = nio.RoomMessageText,
             room_id       = room_id,
-            event_id      = "local_echo",
+            event_id      = f"local_echo.{uuid4()}",
             sender_id     = self.user_id,
             date          = datetime.now(),
             content       = content["formatted_body"],
             is_local_echo = True,
         )
 
-        await self.room_send(room_id, "m.room.message", content)
+        async with self.send_locks[room_id]:
+            print(await self.room_send(room_id, "m.room.message", content))
 
 
     # Callbacks for nio responses

src/qml/Chat/Timeline/EventList.qml

@@ -37,8 +37,11 @@ HRectangle {
         // Declaring this "alias" provides the on... signal
         property real yPos: visibleArea.yPosition
 
+        property int zz: 0
         onYPosChanged: {
             if (chatPage.category != "Invites" && yPos <= 0.1) {
+                zz += 1
+                print(zz)
                 //Backend.loadPastEvents(chatPage.roomId)
             }
         }