fix(sidepanel): autofocus prompt input on open for desktop only (#2857)

Focus the prompt textarea when the sidepanel opens, skipping mobile
to avoid triggering the virtual keyboard which disrupts the layout.
Blur the input when the sidepanel closes to remove lingering focus.

Author: 8bittitan

packages/docsearch-react/src/Sidepanel/Sidepanel.tsx

@@ -6,6 +6,7 @@ import { AlgoliaLogo, type AlgoliaLogoTranslations } from '../AlgoliaLogo';
 import type { DocSearchSidepanelProps, SidepanelSearchParameters } from '../Sidepanel';
 import type { StoredAskAiState, SuggestedQuestionHit } from '../types';
 import { useAskAi } from '../useAskAi';
+import { useIsMobile } from '../useIsMobile';
 import { useSearchClient } from '../useSearchClient';
 import { useSuggestedQuestions } from '../useSuggestedQuestions';
 import { buildDummyAskAiHit } from '../utils/ai';
@@ -159,6 +160,7 @@ function SidepanelInner(
   const [stoppedStreaming, setStoppedStreaming] = React.useState(false);
   const sidepanelContainerRef = React.useRef<HTMLDivElement>(null);
   const promptInputRef = React.useRef<HTMLTextAreaElement>(null);
+  const isMobile = useIsMobile();
 
   const expectedWidth = useSidepanelWidth({
     isExpanded,
@@ -342,11 +344,19 @@ function SidepanelInner(
     }
   }, [initialMessage, sendMessage, conversations, handleSelectConversation, setMessages]);
 
-  // eslint-disable-next-line no-warning-comments
-  // FIX: Renable autofocus on open once mobile focus issue is solved
-  // React.useEffect(() => {
-  //   promptInputRef.current?.focus();
-  // }, [isOpen]);
+  // Autofocus the prompt input when the sidepanel opens and blur it when
+  // it closes. Disabled on mobile because focusing the textarea triggers the
+  // virtual keyboard which disrupts the layout — this is a known issue that
+  // has not been resolved yet.
+  React.useEffect(() => {
+    if (isOpen && !isMobile) {
+      promptInputRef.current?.focus();
+    }
+
+    if (!isOpen) {
+      promptInputRef.current?.blur();
+    }
+  }, [isOpen, isMobile]);
 
   return (
     <div