Fix/Socket reconnection rehydrates

reflex/app.py

@@ -2082,17 +2082,42 @@ async def on_connect(self, sid: str, environ: dict):
         if isinstance(self._token_manager, RedisTokenManager):
             # Make sure this instance is watching for updates from other instances.
             self._token_manager.ensure_lost_and_found_task(self.emit_update)
+
         query_params = urllib.parse.parse_qs(environ.get("QUERY_STRING", ""))
         token_list = query_params.get("token", [])
-        if token_list:
-            await self.link_token_to_sid(sid, token_list[0])
-        else:
+        token = token_list[0] if token_list else None
+
+        if not token:
             console.warn(f"No token provided in connection for session {sid}")
+            return
+
+        try:
+            # Detect reconnect (token seen before)
+            is_reconnect = token in self._token_manager.token_to_sid
+
+            # Always link first to ensure mappings are valid
+            await self.link_token_to_sid(sid, token)
+
+            # If this is a reconnect and backend has lost state, trigger reload
+            if is_reconnect:
+                substate_key = _substate_key(token, self.app.state_manager.state)
+                state = await self.app.state_manager.get_state(substate_key)
+
+                if not getattr(state, "router_data", None):
+                    console.debug(
+                        f"[Reflex] Reconnect detected for expired state (token={token}), emitting reload"
+                    )
+                    await self.emit("reload", {"reason": "state_expired"}, to=sid)
+                    return
+
+        except Exception as e:
+            console.warn(f"[Reflex] on_connect error for token {token}: {e}")
 
         subprotocol = environ.get("HTTP_SEC_WEBSOCKET_PROTOCOL")
         if subprotocol and subprotocol != constants.Reflex.VERSION:
             console.warn(
-                f"Frontend version {subprotocol} for session {sid} does not match the backend version {constants.Reflex.VERSION}."
+                f"Frontend version {subprotocol} for session {sid} "
+                f"does not match backend version {constants.Reflex.VERSION}."
             )
 
     def on_disconnect(self, sid: str) -> asyncio.Task | None: