Line breaks allowed in text input of autoinstall file URL

[eggplants]

Is there an existing issue for this?

• I have searched the existing issues and found none matching what I'm reporting.

Bug Description

Line breaks are allowed in text input of autoinstall file URL.

Steps to reproduce the behavior

1. Select Automated with autoinstall file in "Type of installation" page
2. Go next
3. Enter text containing line breaks in the URL field

Expected behavior

Line breaks are not allowed in text input of autoinstall file URL.

Ubuntu release

Other (specify in the last field)

What architecture are you using?

amd64

System info

ubuntu@ubuntu:~$ uname -rv && snap info ubuntu-desktop-bootstrap snapd
7.0.0-14-generic #14-Ubuntu SMP PREEMPT_DYNAMIC Mon Apr 13 11:09:53 UTC 2026
name:      ubuntu-desktop-bootstrap
summary:   Ubuntu Desktop Bootstrap
publisher: Canonical✓
store-url: https://snapcraft.io/ubuntu-desktop-bootstrap
contact:   https://bugs.launchpad.net/ubuntu-desktop-provision
license:   unset
description: |
  A modern implementation of the Ubuntu Desktop installer.
  It comprises a Flutter-based UI and uses subiquity as the backend.
commands:
  - ubuntu-desktop-bootstrap.curtin
  - ubuntu-desktop-bootstrap.probert
  - ubuntu-desktop-bootstrap.python
  - ubuntu-desktop-bootstrap.subiquity-loadkeys
  - ubuntu-desktop-bootstrap
services:
  ubuntu-desktop-bootstrap.subiquity-server: simple, enabled, active
snap-id:      dLfoSWlQziHta7kJaco3IhnPwGVJ3bIt
tracking:     26.04/stable
refresh-date: 9 days ago, at 11:15 JST
channels:
  latest/stable:    0+git.c03fe36df 2025-11-18 (433) 118MB classic
  latest/candidate: ↑                                      
  latest/beta:      ↑                                      
  latest/edge:      ↑                                      
  26.10/stable:     26.04           2026-04-17 (587) 121MB classic
  26.10/candidate:  ↑                                      
  26.10/beta:       ↑                                      
  26.10/edge:       26.04           2026-04-17 (587) 121MB classic
  26.04/stable:     26.04           2026-04-17 (589) 121MB classic
  26.04/candidate:  ↑                                      
  26.04/beta:       ↑                                      
  26.04/edge:       26.04           2026-04-17 (589) 121MB classic
  25.10/stable:     0+git.31940d804 2025-10-01 (441) 126MB classic
  25.10/candidate:  ↑                                      
  25.10/beta:       ↑                                      
  25.10/edge:       0+git.a19f971fc 2025-10-02 (443) 126MB classic
  25.04/stable:     0+git.1b7778803 2025-07-29 (409) 115MB classic
  25.04/candidate:  ↑                                      
  25.04/beta:       ↑                                      
  25.04/edge:       0+git.1b7778803 2025-07-28 (409) 115MB classic
  24.10/stable:     0+git.8f7b50565 2024-10-08 (290) 112MB classic
  24.10/candidate:  ↑                                      
  24.10/beta:       ↑                                      
  24.10/edge:       0+git.8f7b50565 2024-10-08 (290) 112MB classic
  24.04/stable:     24.04.4.1       2026-04-10 (572) 119MB classic
  24.04/candidate:  ↑                                      
  24.04/beta:       ↑                                      
  24.04/edge:       24.04.4.1       2026-04-10 (572) 119MB classic
installed:          26.04                      (589) 121MB classic
---
name:      snapd
summary:   Daemon and tooling that enable snap packages
publisher: Canonical✓
store-url: https://snapcraft.io/snapd
license:   GPL-3.0
description: |
  Install, configure, refresh and remove snap packages. Snaps are
  'universal' packages that work across many different Linux systems,
  enabling secure distribution of the latest apps and utilities for
  cloud, servers, desktops and the internet of things.
 
  Start with 'snap list' to see installed snaps.
type:         snapd
snap-id:      PMrrV4ml8uWuEUDBT8dSGnKUYbevVhc4
tracking:     latest/stable
refresh-date: 9 days ago, at 10:21 JST
channels:
  latest/stable:          2.75.2                   2026-04-22 (26865) 51.7MB -
  latest/candidate:       2.75.2                   2026-04-13 (26865) 51.7MB -
  latest/beta:            2.75.2                   2026-04-01 (26865) 51.7MB -
  latest/edge:            2.75.2+g266.a20b2ea      2026-04-30 (27159) 52.4MB -
  fips-updates/stable:    –                                                  
  fips-updates/candidate: –                                                  
  fips-updates/beta:      –                                                  
  fips-updates/edge:      2.75.2+g266.a20b2ea+fips 2026-04-30 (27164) 56.0MB -
installed:                2.75.2                              (26865) 51.7MB snapd

Additional context

minLines / maxLines should be 1, maybe?

ubuntu-desktop-provision/apps/ubuntu_bootstrap/lib/pages/autoinstall/autoinstall_direct_page.dart

Line 47 in 1c038c2

maxLines: null,