v4: a handle with this instance's own host names the local user — another instance writes bob from here as bob@gerbeur.example, so a mention or a link copied from there named no one here: /@bob@gerbeur.example was a 404, and the mention notified nobody. localHandle (shared/validation.ts) drops this instance's host, its API's or its pages', from a handle; resolveUsername reads names by it, so the page, the API and the Open Graph 301 reach bob at /@bob, and so do the mention notifications and the chat's highlight and chime.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/test/services/notification-service.test.ts

@@ -15,6 +15,7 @@ test("mentions: notify the named, once per context, never the author or an email
   const named = await createUser();
   const { id: dumpId } = insertDump({ userId: author.id, title: "Topic" });
   const body = `hi @${named.username.toUpperCase()} and @${named.username}, ` +
+    `@${named.username}@gerbeur.test as another instance writes them, ` +
     `me @${author.username}, mail x@${named.username}.com, ` +
     `[@${named.username}](link) @nobody_known`;
   const c = await post<Comment>(`/api/dumps/${dumpId}/comments`, {