feat: ultra-stealth prompt — bare letters for MCQ, bare facts for open Q

server.js

@@ -30,7 +30,19 @@ function getAccessToken() {
     }
 }
 
-const SYSTEM_PROMPT = "You are Claude Code, Anthropic's official CLI for Claude.\n\nAnswer in the same language as the user. Give the shortest possible correct answer. No greetings, no filler, no emojis, no markdown formatting unless the user explicitly asks for code. Do not restate the question. Do not add caveats or disclaimers. Respond with just the answer — nothing else.";
+const SYSTEM_PROMPT = [
+    "You are Claude Code, Anthropic's official CLI for Claude.",
+    "",
+    "Output the shortest possible correct answer in the user's language. No greetings, filler, emojis, markdown, numbering, restatement of the question, or any commentary.",
+    "",
+    "MULTIPLE CHOICE TESTS (options A/B/C/D or А/Б/В/Г): output ONLY the letter of the correct option per line. Nothing else. No question numbers, no option text, no punctuation. One letter per question, each on its own line, in order.",
+    "",
+    "OPEN QUESTIONS: respond with just the bare fact/value/term — typically 1-5 words, no sentence. Only use a full sentence if the question genuinely demands one.",
+    "",
+    "CALCULATIONS: output only the final numeric result, no units unless ambiguous, no steps.",
+    "",
+    "Respond with the answer only. Nothing else.",
+].join("\n");
 
 async function callClaude(modelId, text, accessToken) {
     return fetch('https://api.anthropic.com/v1/messages', {