docs: address Greptile + Cursor review on Ask AI

- Guard req.json() with try/catch → 400 on malformed body (was 500)
- Scope vector search to the reader's locale (mirrors site search); client
  forwards the active locale to the route
- Backstop the whole serialized payload so assistant/tool parts can't be
  stuffed past the user-text cap
- Split the scroll effect: instant jump on panel open, smooth on new messages
- Add rel="noopener noreferrer" target="_blank" to source-chip links

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ouiliame

apps/docs/app/[lang]/layout.tsx

@@ -121,7 +121,7 @@ export default async function Layout({ children, params }: LayoutProps) {
           >
             {children}
           </DocsLayout>
-          <AskAI />
+          <AskAI locale={lang} />
         </RootProvider>
       </body>
     </html>

apps/docs/app/api/chat/route.ts

@@ -14,6 +14,24 @@ const CHAT_MODEL = process.env.OPENAI_CHAT_MODEL || 'gpt-5.4-mini'
 /** Max documentation chunks returned per search to ground an answer. */
 const SEARCH_LIMIT = 6
 
+/** Candidates pulled before locale filtering, so a locale still yields SEARCH_LIMIT results. */
+const SEARCH_CANDIDATES = SEARCH_LIMIT * 4
+
+/** Locales the docs are published in (mirrors the site search route). */
+const KNOWN_LOCALES = ['en', 'es', 'fr', 'de', 'ja', 'zh']
+const DEFAULT_LOCALE = 'en'
+
+/**
+ * Match a chunk's source document to a locale, mirroring the site search route:
+ * non-English docs are prefixed with their locale segment; unprefixed docs are
+ * English.
+ */
+function matchesLocale(sourceDocument: string, locale: string): boolean {
+  const firstSegment = sourceDocument.split('/')[0]
+  if (KNOWN_LOCALES.includes(firstSegment)) return firstSegment === locale
+  return locale === DEFAULT_LOCALE
+}
+
 /**
  * Abuse guards. This endpoint proxies a paid LLM, so an unauthenticated public
  * route is a target for scripted "free inference". These bounds cap the cost of
@@ -28,6 +46,8 @@ const MAX_MESSAGES = 200
 const MAX_USER_INPUT_CHARS = 400_000
 const MAX_OUTPUT_TOKENS = 4000
 const MAX_STEPS = 6
+/** Backstop on the whole serialized payload — blocks stuffing assistant/tool parts past the user-text cap. */
+const MAX_TOTAL_CHARS = 1_000_000
 
 /** Total length of user-authored text across the conversation. */
 function userInputChars(messages: UIMessage[]): number {
@@ -84,7 +104,7 @@ Guidelines:
  * Vector search over the docs embeddings, returning the most relevant chunks
  * with their source links so the model can ground and cite its answer.
  */
-async function searchDocs(query: string) {
+async function searchDocs(query: string, locale: string) {
   const embedding = await generateSearchEmbedding(query)
   const vectorLiteral = JSON.stringify(embedding)
 
@@ -93,32 +113,47 @@ async function searchDocs(query: string) {
       title: docsEmbeddings.headerText,
       url: docsEmbeddings.sourceLink,
       content: docsEmbeddings.chunkText,
-      similarity: sql<number>`1 - (${docsEmbeddings.embedding} <=> ${vectorLiteral}::vector)`,
+      sourceDocument: docsEmbeddings.sourceDocument,
     })
     .from(docsEmbeddings)
     .orderBy(sql`${docsEmbeddings.embedding} <=> ${vectorLiteral}::vector`)
-    .limit(SEARCH_LIMIT)
-
-  return rows.map((row) => ({
-    title: row.title,
-    url: row.url,
-    content: row.content,
-  }))
+    .limit(SEARCH_CANDIDATES)
+
+  return rows
+    .filter((row) => matchesLocale(row.sourceDocument, locale))
+    .slice(0, SEARCH_LIMIT)
+    .map((row) => ({
+      title: row.title,
+      url: row.url,
+      content: row.content,
+    }))
 }
 
 export async function POST(req: Request) {
   if (!isAllowedOrigin(req)) {
     return new Response('Forbidden', { status: 403 })
   }
 
-  const { messages }: { messages: UIMessage[] } = await req.json()
+  let body: { messages: UIMessage[]; locale?: string }
+  try {
+    body = await req.json()
+  } catch {
+    return new Response('Invalid JSON', { status: 400 })
+  }
+  const { messages } = body
+  const locale = KNOWN_LOCALES.includes(body.locale ?? '')
+    ? (body.locale as string)
+    : DEFAULT_LOCALE
 
   if (!Array.isArray(messages) || messages.length === 0 || messages.length > MAX_MESSAGES) {
     return new Response('Invalid request', { status: 400 })
   }
   if (userInputChars(messages) > MAX_USER_INPUT_CHARS) {
     return new Response('Request too large', { status: 413 })
   }
+  if (JSON.stringify(messages).length > MAX_TOTAL_CHARS) {
+    return new Response('Request too large', { status: 413 })
+  }
 
   const result = streamText({
     model: openai(CHAT_MODEL),
@@ -133,7 +168,7 @@ export async function POST(req: Request) {
         inputSchema: z.object({
           query: z.string().describe('A focused natural-language search query.'),
         }),
-        execute: async ({ query }) => searchDocs(query),
+        execute: async ({ query }) => searchDocs(query, locale),
       }),
     },
   })

apps/docs/components/ai/ask-ai.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { type FormEvent, useEffect, useRef, useState } from 'react'
+import { type FormEvent, useEffect, useMemo, useRef, useState } from 'react'
 import { useChat } from '@ai-sdk/react'
 import { DefaultChatTransport } from 'ai'
 import { ArrowUp, MessageCircle, Square, X } from 'lucide-react'
@@ -40,20 +40,35 @@ function getText(parts: ReadonlyArray<{ type: string; [key: string]: unknown }>)
     .join('')
 }
 
-export function AskAI() {
+interface AskAIProps {
+  /** Active docs locale, forwarded so retrieval is scoped to the reader's language. */
+  locale: string
+}
+
+export function AskAI({ locale }: AskAIProps) {
   const [open, setOpen] = useState(false)
   const [input, setInput] = useState('')
   const scrollRef = useRef<HTMLDivElement>(null)
 
-  const { messages, sendMessage, status, stop, error } = useChat({
-    transport: new DefaultChatTransport({ api: '/api/chat' }),
-  })
+  const transport = useMemo(
+    () => new DefaultChatTransport({ api: '/api/chat', body: { locale } }),
+    [locale]
+  )
+
+  const { messages, sendMessage, status, stop, error } = useChat({ transport })
 
   const isBusy = status === 'submitted' || status === 'streaming'
 
+  // Jump to the bottom instantly when the panel opens (a mount transition).
+  useEffect(() => {
+    if (!open) return
+    scrollRef.current?.scrollTo({ top: scrollRef.current.scrollHeight })
+  }, [open])
+
+  // Smooth-scroll as new messages stream in (an explicit re-orientation cue).
   useEffect(() => {
     scrollRef.current?.scrollTo({ top: scrollRef.current.scrollHeight, behavior: 'smooth' })
-  }, [messages, open])
+  }, [messages])
 
   const handleSubmit = (event: FormEvent) => {
     event.preventDefault()
@@ -133,6 +148,8 @@ export function AskAI() {
                         <a
                           key={source.url}
                           href={source.url}
+                          target='_blank'
+                          rel='noopener noreferrer'
                           className='rounded-md border border-[var(--border-1)] px-2 py-0.5 text-[var(--text-muted)] text-xs transition-colors hover:bg-[var(--surface-active)]'
                         >
                           {source.title || source.url}