perf(oauth): Redis-cache getTokenCustomer to eliminate uncached DB hit on every ChatGPT API call

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/oauth.ts

@@ -1,6 +1,7 @@
 import crypto from 'crypto';
 import type { RowDataPacket } from 'mysql2/promise';
 import { getPool, isPoolReady } from './db.js';
+import redis from './redis.js';
 
 const AUTH_CODE_EXPIRY_MS = 10 * 60 * 1000; // 10 minutes
 const TOKEN_EXPIRY_MS = 24 * 60 * 60 * 1000; // 24 hours
@@ -298,13 +299,19 @@ export async function validateAccessToken(tokenValue: string): Promise<boolean>
 
 export async function getTokenCustomer(tokenValue: string): Promise<{ customerId: string } | null> {
   try {
+    const cacheKey = `oauth:token:${tokenValue}`;
+    const cached = await redis.get(cacheKey);
+    if (cached) return { customerId: cached };
+
     const pool = getPool();
     const [rows] = await pool.execute<RowDataPacket[]>(
       'SELECT customer_id FROM oauth_tokens WHERE token = ? AND expires_at > NOW()',
       [tokenValue]
     );
     if (!Array.isArray(rows) || rows.length === 0 || !rows[0].customer_id) return null;
-    return { customerId: rows[0].customer_id as string };
+    const customerId = rows[0].customer_id as string;
+    await redis.setEx(cacheKey, 60, customerId);
+    return { customerId };
   } catch (err) {
     console.error('[oauth] getTokenCustomer error:', err);
     return null;