### System details

#   Lenovo Yoga C640 (81UE), Intel i7-10510U, kernel 7.1.5-arch1-2,  #   omarchy-dev 4.0.0.r1541.gfd1034f (edge) — upgraded from Omarchy 3.8.4

### What's wrong?

While re-running `omarchy-upgrade-to-quattro`, the keyring step failed and could not
recover, no matter how many times the package was deleted and re-downloaded:

```
:: File /var/cache/pacman/pkg/omarchy-keyring-20251027-1-any.pkg.tar.zst is corrupted
   (invalid or corrupted package (checksum)).
Do you want to delete it? [Y/n]
error: failed to commit transaction (invalid or corrupted package (checksum))
Errors occurred, no packages were upgraded.
Warning: Keyring package install failed; attempting to trust the Omarchy packaging key directly.
gpg: key F0134EE680CAC571: "Omarchy <[email protected]>" not changed
  -> Locally signed 1 key.
:: Synchronizing package databases...
 omarchy is up to date
warning: omarchy-keyring-20251027-1 is up to date -- reinstalling
...
:: File /var/cache/pacman/pkg/omarchy-keyring-20251027-1-any.pkg.tar.zst is corrupted
error: failed to commit transaction (invalid or corrupted package (checksum))
```

The freshly downloaded file fails the same way every time. Not a mirror problem and not
disk space (129 GB free, and the download completes).

**Cause.** `install_keyrings()` already documents the underlying situation:

> Pre-quattro installs cached omarchy packages downloaded from the legacy repo. The quattro
> package server rebuilds some of them under the same name and version with different bytes,
> so the cached copies fail the new database's checksum…

…and it deletes the cached `omarchy-*` files. But the recovery then runs:

```bash
as_root pacman -Sy --noconfirm archlinux-keyring omarchy-keyring
```

`-Sy` **skips refreshing a database it believes is current** — note `omarchy is up to date`
in the output above. So the local db keeps the *old* checksum for a package the server has
rebuilt, and rejects the correct bytes indefinitely. Clearing the package cache can't help,
because the stale data is in the *database*, not the cache.

**Workaround**

```bash
sudo pacman -Syy          # double y forces the databases to re-download
bash ~/upgrade-to-quattro.sh --dev
```

After that the keyring step passed immediately and the upgrade ran to completion.

**Suggestion.** Use `pacman -Syy` in `install_keyrings` (at least on the retry path). Since
"rebuilt under the same name and version" is a known property of the package server, forcing
a database refresh there seems like the direct fix — otherwise the failure is unrecoverable
without the user knowing the `-Syy` trick.