fix: add type annotation for ChatCompletionMessageParam in getHint and tutorChat functions

backend/src/services/aiAssist.ts

@@ -1,6 +1,7 @@
 import { z } from 'zod'
 import { getAIClient, getAIModelForTask } from './aiClient.js'
 import { AiUsageResult, estimateTokensFromMessages, estimateTokensFromText, estimateTotalTokens, resolveUsageTokens } from '../utils/aiTokens.js'
+import type { ChatCompletionMessageParam } from 'openai/resources/index.js'
 
 export type QuestionType =
   | 'multiple-choice'
@@ -234,7 +235,7 @@ export async function getHint(req: HintRequest): Promise<AiUsageResult<{ hint: s
   const safeQuestion = stripAnswerFields(req.question)
   const model = getAIModelForTask('hint')
 
-  const messages = [
+  const messages: ChatCompletionMessageParam[] = [
     {
       role: 'system',
       content: `You are a tutor helping a student during an exam. Give exactly one short hint (1-2 sentences) in ${req.language} that nudges the student toward the right approach. Never reveal the answer, never restate the answer in different words, and never give the answer to a multiple-choice option. Focus on the concept or strategy. Respond ONLY with a JSON object: { "hint": string }.`,
@@ -245,7 +246,7 @@ export async function getHint(req: HintRequest): Promise<AiUsageResult<{ hint: s
     },
   ]
 
-  const promptTokens = estimateTokensFromMessages(messages)
+  const promptTokens = estimateTokensFromMessages(messages as Array<{ content: string }>)
   const estimatedTokens = estimateTotalTokens(promptTokens, 160)
 
   const completion = await client.chat.completions.create({
@@ -315,11 +316,11 @@ Exam (JSON): ${JSON.stringify(req.exam).slice(0, 8000)}
 
 Student's submission state (answers, flags, etc., JSON): ${JSON.stringify(req.state).slice(0, 4000)}`
 
-  const messages = [
+  const messages: ChatCompletionMessageParam[] = [
     { role: 'system', content: systemPrompt },
     ...recent.map((m) => ({ role: m.role, content: m.content })),
   ]
-  const promptTokens = estimateTokensFromMessages(messages)
+  const promptTokens = estimateTokensFromMessages(messages as Array<{ content: string }>)
   const estimatedTokens = estimateTotalTokens(promptTokens, 600)
 
   const completion = await client.chat.completions.create({

backend/src/utils/tokens.ts

@@ -10,7 +10,7 @@ export interface JwtPayload {
 }
 
 export function signToken(payload: JwtPayload): string {
-  return jwt.sign(payload, config.jwtSecret, { expiresIn: config.jwtExpiresIn })
+  return jwt.sign(payload, config.jwtSecret, { expiresIn: config.jwtExpiresIn } as jwt.SignOptions)
 }
 
 export function verifyToken(token: string): JwtPayload {