Preserve outbound backlog across outages, fix backoff quiet period

src/HomeAssistant/Runtime/Connection.hs

@@ -15,6 +15,7 @@ import Control.Concurrent.STM
   , writeTChan
   , writeTVar
   )
+import Control.Exception (onException)
 import Control.Exception.Annotated (throw)
 import Control.Lens ((^?))
 import Control.Monad (forever)
@@ -38,7 +39,8 @@ readerAction host port token bus =
     subscribe bus conn
     atomically $ writeTVar (busConn bus) (Just conn)
     putStrLn "[reader] connected"
-    receiveLoop bus conn
+    -- Unpublish on exit so the writer blocks and the backlog survives the outage.
+    receiveLoop bus conn `onException` atomically (writeTVar (busConn bus) Nothing)
 
 handshake :: WS.Connection -> String -> IO ()
 handshake conn token = do