perf: halve Redis round trips on model resolution and socket pools (#27225)

When WEBSOCKET_MANAGER=redis, app.state.MODELS and the socket session/
usage pools are Redis-backed dicts, so every membership test and
getitem is a network round trip:

- generate_chat_completion checked `model_id not in models` (HEXISTS)
  and then read `models[model_id]` (HGET) on every chat completion.
  A single .get() now serves both, with the same not-found error.
- The direct-connection branch spread the pool with `{**MODELS, ...}`,
  which iterates keys() then fetches each value — HKEYS plus one HGET
  per model. dict(MODELS.items()) issues a single HGETALL instead.
- get_user_ids_from_room called SESSION_POOL.get(sid) twice per
  session (once to filter, once for the value); the usage handler
  checked membership then fetched the same key. Both now do one
  lookup.

In non-Redis mode these are plain dicts and behavior is identical.


Claude-Session: https://claude.ai/code/session_01MHg5zs1VBjvRWQ54qHpfYD

Co-authored-by: Claude <noreply@anthropic.com>

backend/open_webui/utils/chat.py

@@ -179,8 +179,10 @@ async def generate_chat_completion(
         # Merge the direct connection model into server models so that
         # task functions (title, tags, etc.) can resolve a server-side
         # task model while still having the direct model available.
+        # dict(...items()) is one HGETALL on a Redis-backed pool; ``{**pool}``
+        # would issue HKEYS plus one HGET per model.
         models = {
-            **request.app.state.MODELS,
+            **dict(request.app.state.MODELS.items()),
             request.state.model['id']: request.state.model,
         }
         log.debug(f'direct connection to model: {request.state.model["id"]}')
@@ -188,11 +190,12 @@ async def generate_chat_completion(
         models = request.app.state.MODELS
 
     model_id = form_data['model']
-    if model_id not in models:
+    # Single lookup — membership check plus getitem would be two Redis
+    # round trips on a Redis-backed model pool.
+    model = models.get(model_id)
+    if model is None:
         raise Exception('Model not found')
 
-    model = models[model_id]
-
     if getattr(request.state, 'direct', False) and model_id == getattr(request.state, 'model', {}).get('id'):
         return await generate_direct_chat_completion(request, form_data, user=user, models=models)
     else: