fix(viewer): preserve archive bootstrap precedence

Author: benvinegar

e2e/embed-archive.spec.ts

@@ -17,7 +17,7 @@ const embedHtml = `<!doctype html>
 <body><div id="m"></div>
 <script type="module">
   import { mountViewer } from "/__embed/engine.js";
-  let route = { archives: true };
+  let route = { archives: true, surfaceId: "stale-post-id" };
   const subscribers = new Set();
   window.__archiveRoute = (next) => {
     route = next;

viewer/src/state.ts

@@ -215,7 +215,9 @@ function syntheticSession(id: string): SessionRow {
 // user lands somewhere usable rather than a blank page.
 export async function bootstrap() {
   const route = host().router.get();
-  if (route.surfaceId && !route.sessionId) {
+  // Keep archive precedence consistent with applyRoute() and the default
+  // router: an embedding host may leave a stale surfaceId on its archive route.
+  if (!route.archives && route.surfaceId && !route.sessionId) {
     await enterStandalone(route.surfaceId);
     if (standalonePost()) return;
   }