An update you can ask for, and a boundary that stays where it was

The button cannot do the work, and that is the whole design. The service runs as
an unprivileged account, cannot restart itself, and should not be able to: a web
application that can restart its own service is one whose worst day is much
worse. So /admin/updates writes a file, and an opt-in systemd .path unit runs
deploy/update.sh as root.

Three properties hold it up, and each is a thing that could have been got wrong.
The request file carries nothing that reaches a command line -- no branch, no
ref, no arguments -- because the branch is baked into the unit at install time,
so pressing the button is always "deploy the branch this host was configured
with" and can never be "deploy something else". It is off unless somebody passes
INSTALL_UPDATE_HELPER=1, and re-running the installer without it removes both
units and the marker. And without the helper the page says so and prints the
manual command rather than writing a file nothing is watching, which would be a
button that reports success and does nothing.

The card that says all of this is rendered whether or not there is anything to
apply. It was inside the "there is an update" branch first, so an administrator
could not discover the helper was missing until the day they needed it, which is
the worst possible moment.

Opening the page makes no network request; Check is the one thing that fetches.
And it shows the log between, not a count: "3 behind" is a number somebody has to
go and look up, while the subjects are what decides whether this is worth
restarting for right now.

Docker is one stage, because there is nothing to build -- no Node, no compiled
assets. It bakes no secret key (one in an image is one every copy shares, and
rotating it makes stored API keys unreadable), no data, and no .git, so
/admin/updates inside a container correctly reports that it was not installed
from a checkout. Compose publishes on loopback and refuses to start without a
key. TLS in front is a constraint rather than a recommendation: the service
worker and the microphone both require HTTPS or localhost.

The image was built and run before this was committed, which is how the missing
COPY of LICENSE was found -- pyproject declares it and the build backend reads
it, so the failure reads like a packaging problem and is one line.

deploy/lxc-install.sh creates an unprivileged Debian container and runs the
existing installer inside it. A wrapper, not a second install path: a parallel
installer is two things to keep correct and one of them rots.

/healthz opens the database rather than only proving the socket is listening -- a
process that is up with a database it cannot open answers every page with a 500
-- and says nothing about what is here, being reachable without signing in.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

deploy/lembas-update.service

@@ -0,0 +1,37 @@
+# Runs deploy/update.sh when the web interface asks for it.
+#
+# install.sh substitutes __PREFIX__, __SERVICE_USER__ and __UPDATE_BRANCH__ and
+# writes the result to /etc/systemd/system/lembas-update.service.
+#
+# **What this grants.** Installing it means anybody who can administer the web
+# interface can deploy whatever is on the configured branch, as root, and
+# restart the service. That is the point of it, and it is why it is opt-in and
+# why the installer says so out loud rather than doing it by default.
+#
+# **What it deliberately does not grant.** The request file carries nothing that
+# reaches this command line: no branch, no ref, no arguments. The branch is
+# baked in below, from the installer's environment, so pressing the button is
+# "deploy the branch this host was configured with" and can never be "deploy
+# something else".
+
+[Unit]
+Description=Apply a requested LLeMbas update
+# Not `After=lembas.service`: this restarts it, and an ordering dependency on
+# the thing being restarted is how a one-shot ends up waiting for itself.
+
+[Service]
+Type=oneshot
+# Deleted first, always. The path unit re-arms on the file existing, so leaving
+# it in place would run this again the moment the service came back -- an
+# update loop with no obvious cause. `-` so a failure to delete does not stop
+# the update, and `ExecStartPre` so it happens even if the script itself fails.
+ExecStartPre=-/usr/bin/rm -f __PREFIX__/data/update-requested
+Environment=SERVICE_USER=__SERVICE_USER__
+Environment=PREFIX=__PREFIX__
+Environment=LEMBAS_BRANCH=__UPDATE_BRANCH__
+ExecStart=/bin/bash __PREFIX__/app/deploy/update.sh
+# The script's own failure path prints the journal and exits non-zero, which is
+# what makes `systemctl status lembas-update` say what went wrong.
+StandardOutput=journal
+StandardError=journal
+TimeoutStartSec=600