docs: relax Ask AI request caps; count only user-authored input

The size cap previously measured the whole serialized message array, so a
follow-up question failed (413) once the history carried the prior answer plus
retrieved doc chunks. Count only user-authored text instead, and loosen all
bounds ~20x so normal multi-turn use never hits them — they remain only as a
backstop against egregious abuse.

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

Author: ouiliame

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

@@ -19,11 +19,27 @@ const SEARCH_LIMIT = 6
  * route is a target for scripted "free inference". These bounds cap the cost of
  * any single request; durable per-IP rate limiting, a provider spend cap, and
  * edge bot protection are provisioned separately (see the PR checklist).
+ *
+ * The size cap counts only user-authored text — NOT the conversation history,
+ * assistant turns, or retrieved doc chunks we add via the searchDocs tool, which
+ * legitimately grow large over a multi-turn chat.
  */
-const MAX_MESSAGES = 30
-const MAX_INPUT_CHARS = 12_000
-const MAX_OUTPUT_TOKENS = 800
-const MAX_STEPS = 3
+const MAX_MESSAGES = 200
+const MAX_USER_INPUT_CHARS = 400_000
+const MAX_OUTPUT_TOKENS = 4000
+const MAX_STEPS = 6
+
+/** Total length of user-authored text across the conversation. */
+function userInputChars(messages: UIMessage[]): number {
+  let total = 0
+  for (const message of messages) {
+    if (message.role !== 'user') continue
+    for (const part of message.parts) {
+      if (part.type === 'text') total += part.text.length
+    }
+  }
+  return total
+}
 
 /**
  * Reject obvious cross-origin calls. Same-origin browser requests send an
@@ -100,7 +116,7 @@ export async function POST(req: Request) {
   if (!Array.isArray(messages) || messages.length === 0 || messages.length > MAX_MESSAGES) {
     return new Response('Invalid request', { status: 400 })
   }
-  if (JSON.stringify(messages).length > MAX_INPUT_CHARS) {
+  if (userInputChars(messages) > MAX_USER_INPUT_CHARS) {
     return new Response('Request too large', { status: 413 })
   }