fix(v2): use root SSH as bootstrap readiness signal

backend/src/services/deploy.ts

@@ -13,7 +13,7 @@ import {
   deleteKeyPairAws,
   deleteSecurityGroupAws,
 } from "./ec2";
-import { connectSsh, waitForBootstrap, type SshSession } from "./ssh";
+import { connectSsh, type SshSession } from "./ssh";
 import {
   buildPrCommentBody,
   postComment,
@@ -232,8 +232,10 @@ async function firstDeploy(
   activeSshSessions.set(previewId, sshSession);
 
   try {
-    await appendLog(previewId, `[PP] SSH connected. Waiting for bootstrap to complete...\n`);
-    await waitForBootstrap(sshSession, 900_000);
+    // Root SSH is enabled as the final bootstrap step, after the completion
+    // marker is written. A successful root connection is therefore the
+    // readiness signal; polling the same long-lived SSH connection can leave
+    // a completed instance stuck when its exec channel goes stale.
     await appendLog(previewId, `[PP] Bootstrap complete. Starting setup...\n`);
 
     if (repoConfig.aptPackages.length > 0) {