Wait for installer exit and live shell before followup probes

dev/iso-smoke.py

@@ -505,6 +505,17 @@ class Console:
                    re.escape(token.encode()) + rb':INSTALL_EXIT:[0-9]+\x1f')
         return self.expect(pattern, timeout, failure_pattern=failure)
 
+    def finish_installer(self, token, timeout=30):
+        # Completion text can arrive before the process exits and readline
+        # resumes. Input sent during that gap can be discarded by the TTY.
+        deadline = time.monotonic() + timeout
+        returned = self.expect(rb'\x1e' + re.escape(token.encode()) +
+                               rb':INSTALL_EXIT:([0-9]+)\x1f', timeout)
+        status = int(returned.group(1))
+        if status:
+            raise SmokeError(f'Installer returned status {status} after completion')
+        self.expect(rb'hydra-live[^\r\n]*[#$] ', max(0, deadline - time.monotonic()))
+
     def command(self, command, timeout=60):
         token = secrets.token_hex(12)
         self.buffer = b''
@@ -818,6 +829,7 @@ def main(argv=None):
         console.send(password + '\n')
         console.expect_installer(rb'Installation completed\. Diagnostic log: [^\r\n]+',
                                  args.install_timeout, installer_token)
+        console.finish_installer(installer_token)
         checkpoint('real_installer', b'Installer completed via guest controlling TTY')
         console.command("sudo -n mkdir -p /mnt/hydra-validation && sudo -n mount /dev/vda2 /mnt/hydra-validation && printf %s " +
                         shlex.quote(sentinel) + " | sudo -n tee /mnt/hydra-validation/var/lib/hydra-acceptance-sentinel >/dev/null && sudo -n umount /mnt/hydra-validation", 60)