fix(telegram): final message waits for the draft push in flight

src/beaver_gateway/frontends/telegram/drafts.py

@@ -52,6 +52,7 @@ class Draft:
         self._broken = False
         self._last_sent = 0.0
         self._task: asyncio.Task[None] | None = None
+        self._inflight: asyncio.Future[None] | None = None
 
     def start(self) -> None:
         if self._task is None:
@@ -68,17 +69,26 @@ class Draft:
             self._dirty = True
 
     async def stop(self) -> None:
+        """Stop pushing and wait for the push in flight.
+
+        The final ``sendMessage`` must reach Telegram after the last draft,
+        or the draft lands on top of the message and lingers for its 30 s.
+        """
         if self._task is None:
             return
         self._task.cancel()
         with contextlib.suppress(asyncio.CancelledError):
             await self._task
         self._task = None
+        if self._inflight is not None:
+            with contextlib.suppress(Exception):
+                await self._inflight
 
     async def _run(self) -> None:
         while not self._broken:
             if self._dirty or time.monotonic() - self._last_sent > _KEEPALIVE:
-                await self._push()
+                self._inflight = asyncio.ensure_future(self._push())
+                await asyncio.shield(self._inflight)
             await asyncio.sleep(self._interval)
 
     async def _push(self) -> None: