Bind Reddit and Matrix session identities

extensions/reddit-session-exporter/session-export.js

@@ -1,5 +1,26 @@
 const REDDITBOT_SESSION_FILENAME = 'redditbot-session.json';
 
+export function normalizeRedditAccountId(accountId) {
+  const trimmed = String(accountId ?? '').trim();
+  const normalized = trimmed.startsWith('t2_') ? trimmed : `t2_${trimmed}`;
+  if (!/^t2_[a-z0-9]+$/i.test(normalized)) {
+    throw new Error('Reddit returned an invalid account ID.');
+  }
+  return normalized;
+}
+
+export function assertMatchingSessionIdentity(redditIdentity, matrixUserId) {
+  const accountId = normalizeRedditAccountId(redditIdentity?.accountId);
+  const username = String(redditIdentity?.username ?? '').trim();
+  if (!username) throw new Error('Reddit did not return an authenticated username.');
+  const expectedMatrixUserId = `@${accountId}:reddit.com`;
+  if (matrixUserId !== expectedMatrixUserId) {
+    throw new Error(
+      `Reddit is logged in as u/${username} (${accountId}), but Chat is authenticated as ${matrixUserId}. Reload Reddit Chat after switching accounts, then export again.`,
+    );
+  }
+}
+
 function isRedditDomain(domain) {
   const normalised = domain.toLowerCase().replace(/^\./, '');
   return normalised === 'reddit.com' || normalised.endsWith('.reddit.com');