fix: invalidate the RedisDict write signature on batch delete

RedisDict.set() skips the write when the payload fingerprint matches the last one this process wrote, so a mutation that goes around set() has to clear that fingerprint. The new batch delete did not, leaving a stale fingerprint behind: the next refresh with identical content is treated as already written and silently skipped, so the hash stays empty.

Renamed pop_many to delete_many. In a dict emulation pop removes and returns; this returns nothing and cannot without an extra HMGET, so the name promised something it does not do. delete_many matches __delitem__ and the HDEL underneath. Its only call site is the session pool reaper, whose behaviour is unchanged: same fields deleted, same batching, same return.

backend/open_webui/socket/main.py

@@ -206,7 +206,7 @@ async def periodic_session_pool_cleanup():
                     if expired:
                         log.warning('Reaping %d orphaned session(s) from the session pool', len(expired))
                         if WEBSOCKET_MANAGER == 'redis':
-                            SESSION_POOL.pop_many(*expired)
+                            SESSION_POOL.delete_many(*expired)
                         else:
                             for sid in expired:
                                 SESSION_POOL.pop(sid, None)

backend/open_webui/socket/utils.py

@@ -115,10 +115,11 @@ class RedisDict:
             if cursor == 0:
                 break
 
-    def pop_many(self, *keys):
+    def delete_many(self, *keys):
         """Delete fields in one HDEL; no keys is a no-op (HDEL rejects an empty field list)."""
         if keys:
             self.redis.hdel(self.name, *keys)
+            self._last_signature = None
 
     def set(self, mapping: dict):
         if not mapping: