Say an update is running before it starts, not only after

Asked what happens if someone shuts the laptop down mid-update, the honest
answer turned out to be poor. The inhibitor does stop them - logind refuses and
falls back to org.freedesktop.login1.power-off-ignore-inhibit, which is
auth_admin_keep - so the desktop answers with an administrator password prompt
reading "Power off the system while an application is inhibiting this". systemd
ships that string untranslated, it never mentions updates, and no KDE catalog
contains any shutdown-blocked text at all. Only systemctl names the reason.

So a notification now goes out before the transaction, asking for the machine to
be left on. Notifications gained a tag: the result replaces the start message in
place rather than stacking a second, contradictory bubble beside it.

Tagged notifications also carry a queue flag. "An update is starting" is only
meaningful while somebody is looking, so unlike the result it is not spooled for
delivery at next login.

README.md

@@ -127,10 +127,22 @@ unheld on several consecutive runs, you get a notification instead.
 
 Three layers, in order of how much they can actually promise:
 
+**A notification goes out before the transaction starts** — "Installing
+updates, please leave the computer switched on until this is done" — and is
+replaced in place by the result when the run finishes, so it costs one bubble
+rather than two. This exists because of what the next paragraph does *not* do.
+
 **Suspend and a normal shutdown are blocked.** The run holds a
-`systemd-inhibit --what=sleep:shutdown --mode=block` lock, so closing the lid,
-picking "Shut down" from the menu or a short press of the power button will not
-interrupt a transaction — the desktop says something is still busy instead.
+`systemd-inhibit --what=sleep:shutdown --mode=block` lock, so closing the lid or
+picking "Shut down" cannot interrupt a transaction. Be aware of what that looks
+like, though: logind refuses the request and requires the polkit action
+`org.freedesktop.login1.power-off-ignore-inhibit`, which is `auth_admin_keep`.
+The desktop therefore answers a shutdown attempt with an **administrator
+password prompt** reading *"Power off the system while an application is
+inhibiting this"* — a string systemd ships untranslated, and one that never
+mentions updates. No KDE dialog explains the situation. Only `systemctl
+poweroff` in a terminal names the reason. That prompt is exactly why the
+notification above is on by default.
 
 **A hard power-off cannot be prevented by anything.** Holding the power button
 or pulling the plug cuts power in firmware. What limits the damage is that