fix(chat): keep mode switch selection without auto rollback

app/(chat)/page.tsx

@@ -116,14 +116,10 @@ async function NewChatPage() {
   const cookieModel = initialModelId
     ? visibleModels.find(({ model }) => model.id === initialModelId)
     : undefined;
-  const cookieIsVideoModel = Boolean(
-    cookieModel && VIDEO_PROVIDER_TYPES.has(cookieModel.provider.type)
-  );
 
   if (
     !initialModelId ||
-    !cookieModel ||
-    (cookieIsVideoModel && Boolean(nanoBananaModel))
+    !cookieModel
   ) {
     if (nanoBananaModel) {
       initialModelId = nanoBananaModel.model.id;

components/multimodal-input.tsx

@@ -1529,8 +1529,13 @@ function PureModelSelectorCompact({
   useEffect(() => {
     if (displayModels.length === 0) return;
 
-    const currentExists = displayModels.some((m) => m.id === selectedModelId);
-    if (currentExists) return;
+    const currentExistsInDisplay = displayModels.some((m) => m.id === selectedModelId);
+    if (currentExistsInDisplay) return;
+
+    const currentExistsInAll = allModels.some((m) => m.id === selectedModelId);
+    if (currentExistsInAll) {
+      return;
+    }
 
     const fallbackImageModel =
       modeFilteredModels.find((model) => isNanoBananaProModel(model)) ||
@@ -1546,7 +1551,7 @@ function PureModelSelectorCompact({
     startTransition(() => {
       saveChatModelAsCookie(fallbackModelId);
     });
-  }, [canShowAutoModel, displayModels, modeFilteredModels, onModelChange, selectedModelId]);
+  }, [allModels, canShowAutoModel, displayModels, modeFilteredModels, onModelChange, selectedModelId]);
 
   // 自动选择模型的逻辑 - 必须在所有条件 return 之前定义
   const selectBestModel = useCallback(() => {