Evict cache per user agent

src/middleware/cacheBuster.js

@@ -1,21 +1,27 @@
+import crypto from 'node:crypto';
+import { DEFAULT_USER } from '../constants.js';
+
 /**
  * Middleware to bust the browser cache for the current user.
  * @returns {import('express').RequestHandler}
  */
 export default function getCacheBusterMiddleware() {
     /**
-     * @type {Set<string>} Handles that have already been busted.
+     * @type {Set<string>} Handles/User-Agents that have already been busted.
      */
-    const handles = new Set();
+    const keys = new Set();
 
     return (request, response, next) => {
-        const handle = request.user?.profile?.handle;
+        const handle = request.user?.profile?.handle || DEFAULT_USER.handle;
+        const userAgent = request.headers['user-agent'] || '';
+        const hash = crypto.createHash('sha256').update(userAgent).digest('hex');
+        const key = `${handle}-${hash}`;
 
-        if (!handle || handles.has(handle)) {
+        if (keys.has(key)) {
             return next();
         }
 
-        handles.add(handle);
+        keys.add(key);
         response.setHeader('Clear-Site-Data', '"cache"');
         next();
     };