ubuntu-desktop-installer: crash on initial dialog when network unconnected

When launching the ubuntu-desktop-installer from daily canary images, there is an immediate crash report due to a timeouterror during device probe on laptops which are not connected yet to a wireless access point or hardwired ethernet connection.

This looks to be nameserver resolution errors in device prober and snap interactions.

reproducer:
ubuntu-desktop-installer: version: 0+git.74cbf061 revision: 560
Lenovo T14 without RJ45 ethernet plugged in and no wi-fi configured yet

Snippets of log failures:

from journalctl -b 0:

Jul 25 22:12:23 ubuntu os-prober[3844]: debug: running /usr/lib/os-probes/mounted/90linux-distro on mounted /dev/sda4
Jul 25 22:12:23 ubuntu os-prober[3848]: debug: running /usr/lib/os-probes/mounted/90solaris on mounted /dev/sda4
Jul 25 22:12:23 ubuntu kernel: No UUID available providing old NGUID
Jul 25 22:12:25 ubuntu systemd[1868]: Starting Notification regarding a crash report...
Jul 25 22:12:25 ubuntu kernel: No UUID available providing old NGUID
Jul 25 22:12:25 ubuntu systemd[1]: Started crash report submission.
Jul 25 22:12:25 ubuntu whoopsie[3874]: [22:12:25] Using lock path: /var/lock/whoopsie/lock
Jul 25 22:12:25 ubuntu systemd[1]: whoopsie.service: Deactivated successfully.
Jul 25 22:12:25 ubuntu update-notifier-crash[3878]: /usr/bin/whoopsie
Jul 25 22:12:25 ubuntu systemd[1868]: Finished Notification regarding a crash report.
Jul 25 22:12:27 ubuntu systemd[1]: systemd-timedated.service: Deactivated successfully.
...

Jul 25 22:12:58 ubuntu kernel: blk_update_request: I/O error, dev sda, sector 929388 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
Jul 25 22:12:59 ubuntu snapd[1728]: stateengine.go:149: state ensure error: persistent network error: Get https://api.snapcraft.io/api/v1/snaps/sections: dial tcp: lookup api.snapcraft.io: Temporary fai>

From /var/log/installer/subiquity-server-debug.log:

2022-07-25 22:12:10,197 ERROR probert.raid:40 Failed mdadm_assemble, mdadm command not found: [Errno 2] No such file or directory: 'mdadm'
...

2022-07-25 22:12:25,128 ERROR root:37 finish: subiquity/Filesystem/_probe/probe_once: FAIL: cancelled
2022-07-25 22:12:25,129 ERROR block-discover:569 block probing failed restricted=False
Traceback (most recent call last):
  File "/snap/ubuntu-desktop-installer/560/bin/subiquity/subiquity/server/controllers/filesystem.py", line 563, in _probe
    await asyncio.wait_for(self._probe_once_task.task, timeout)
  File "/snap/ubuntu-desktop-installer/560/usr/lib/python3.8/asyncio/tasks.py", line 501, in wait_for
    raise exceptions.TimeoutError()
asyncio.exceptions.TimeoutError
2022-07-25 22:12:25,131 DEBUG subiquity.common.errorreport:384 generating crash report
2022-07-25 22:12:25,147 INFO subiquity.common.errorreport:406 saving crash report 'block probing crashed with TimeoutError' to /var/crash/1658787145.131510019.block_probe_fail.crash
2022-07-25 22:12:25,147 INFO root:37 start: subiquity/ErrorReporter/1658787145.131510019.block_probe_fail/add_info:
2022-07-25 22:12:25,147 DEBUG root:37 start: subiquity/Filesystem/_probe/probe_once: restricted=True
2022-07-25 22:12:25,229 DEBUG urllib3.connectionpool:456 http://localhost:None "GET /v2/changes/4 HTTP/1.1" 200 434
2022-07-25 22:12:25,331 DEBUG urllib3.connectionpool:456 http://localhost:None "GET /v2/changes/4 HTTP/1.1" 200 434
2022-07-25 22:12:25,434 DEBUG curtin:1298 Extracting storage config from probe data
2022-07-25 22:12:25,434 WARNING curtin:424 probe_data missing bcache data

...
 2022-07-25 22:13:39,131 ERROR subiquity.server.controllers.refresh:177 checking for snap update failed
Traceback (most recent call last):
  File "/snap/ubuntu-desktop-installer/560/bin/subiquity/subiquity/server/controllers/refresh.py", line 175, in check_for_update
    result = await self.app.snapd.get('v2/find', select='refresh')
  File "/snap/ubuntu-desktop-installer/560/bin/subiquity/subiquitycore/snapd.py", line 180, in get
    response.raise_for_status()
  File "/snap/ubuntu-desktop-installer/560/lib/python3.8/site-packages/requests/models.py", line 1021, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 500 Server Error: Internal Server Error for url: http+unix://%2Frun%2Fsnapd.socket/v2/find?select=refresh
2022-07-25 22:13:39,132 DEBUG root:37 finish: subiquity/Refresh/check_for_update: SUCCESS: checking for snap update failed

Apologies this needs better triage but I wanted to document this failure path before I'm forced to reboot. Attaching related log files for further debug.