Defined error state when no ui shown

A blank screen or falling back to the bootsplash is never acceptable. To the extent possible, error states should be surfaced and communicate as much state as possible to the user.

This covers cases including but not limited to:

• openpilot never starts up
• openpilot ui crashes

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one example:

harald  [11:28 AM]
I pulled latest master on rivian device and rebooted and got comma logo on screen and no boot. I had the same thing happen in id4 last week, which I then reflashed assuming I did something wrong.
harald  [11:29 AM]
Codex found this:
• Found the likely cause: an incomplete AGNOS 19.7 update.

  - Your new master checkout requires 19.7, but the device still boots 19.6.
  - The staged 19.7 system image fails its checksum, has no completion marker, and its boot slot is marked unbootable.
  - Saved logs show Linux starting, then shutting down after an hour without an openpilot watchdog heartbeat.I was able to put a fixed image on and repair it. But all round pretty frustrating experience.
adeeb  [11:35 AM]
[@Daniel](https://commadotai.slack.com/team/U0A6S0MDVEH) what happened here? updater ui not stating up?
Daniel  [11:36 AM]
looking into it
Daniel  [12:35 PM]
The openpilot updater bundle still had a modem with pyserial dependency that was removed in AGNOS.
fix: https://github.com/commaai/openpilot/compare/fix-bundle