Offer only what this machine can deliver

The installer knew one distribution: Debian, with docker, on a new enough
release. Everything else it would have offered and then failed at.

Three facts now decide what the matrix offers, and each is read from the
machine rather than assumed:

- The container runtime. Docker where the machine has one, podman on the Red
  Hat family, which ships no docker at all. Both go through the same compose
  plugin: compose speaks the Docker API and podman serves it, so there is one
  compose file and one deployment path, not two. Telling a Fedora operator to
  add Docker's own repository to a machine that already has a container
  runtime would have been the wrong trade.

- glibc. The server binary is downloaded, not built here, and it is linked
  against 2.39. Rocky 9 (2.34), Debian 12 and Ubuntu 22.04 cannot run it, so
  the host shape is refused there with the version found and the container
  shape named as the answer -- rather than installing a file that cannot
  start.

- The operating system itself. This compiles for macOS and Windows because Go
  compiles anything, and on either it would read no os-release, find no
  systemd, and describe a machine that does not exist. It now says what it is
  and exits.

Two bugs the other distributions found, both of which Debian could not have:

- The survey reported the first thing in the way and stopped, so on Fedora it
  asked to start podman.socket, and then -- having done it -- asked for the
  compose plugin. Needs are named now, not described, and reported together.

- apply used the survey taken before dependencies were installed, so on a
  machine that had no runtime at all it installed podman and then reached for
  docker. It re-surveys after resolving, and stops if containers still are
  not usable.

The lab takes DISTRO now: debian13, debian12, ubuntu2404, fedora, rocky9,
arch, each with its own disk and ssh port so several can be up at once. The
cases no longer say "docker" either. install-local passes on Debian 13,
Fedora 43 and Rocky 9 -- 20 checks each, ending with a sign-in to the webmail
the installer put there.

e2e/cases/install-public.sh

@@ -26,6 +26,20 @@ MAIL=mx.lab.test          # not "mail": proves the names follow --mail-host
 CONSOLE=console.lab.test
 WEBMAIL=webmail.lab.test
 DIR=/var/lib/inbuxa
+
+# Whichever runtime this machine has. The installer picks docker where there
+# is one and podman on the Red Hat family; a case that says "docker" only
+# tests half the distributions it is run on.
+if command -v docker >/dev/null 2>&1; then
+  RT=docker
+  compose() { docker compose -f "$DIR/compose.yaml" "$@"; }
+else
+  RT=podman
+  compose() {
+    DOCKER_HOST=unix:///run/podman/podman.sock \
+      /usr/local/lib/docker/cli-plugins/docker-compose -f "$DIR/compose.yaml" "$@"
+  }
+fi
 WORK=/tmp/lab
 LABNET=inbuxa-e2e
 LABSUBNET=172.31.254.0/24
@@ -35,7 +49,7 @@ rm -rf "$WORK"; mkdir -p "$WORK"
 
 echo "==> what the installer needs, before the lab"
 /tmp/inbuxa deps --console container --webmail container --install >/dev/null 2>&1 || true
-docker version >/dev/null 2>&1 && ok "docker is usable" || { bad "no docker"; exit 1; }
+{ docker version >/dev/null 2>&1 || podman version >/dev/null 2>&1; } && ok "a container runtime is usable" || { bad "no docker"; exit 1; }
 
 echo
 echo "==> standing up a private CA and a DNS stub"
@@ -145,7 +159,7 @@ CODE=$(curl -s -o /dev/null -w '%{http_code}' --cacert "$WORK/chain.pem" --resol
 
 echo
 echo "==> and nothing was left behind that should not be"
-ENVOUT="$(docker inspect --format '{{range .Config.Env}}{{println .}}{{end}}' "$(docker compose -f $DIR/compose.yaml ps -q server)")"
+ENVOUT="$($RT inspect --format '{{range .Config.Env}}{{println .}}{{end}}' "$(compose ps -q server)")"
 grep -q "RECOVERY_ADMIN" <<<"$ENVOUT" && bad "the server still carries a recovery admin" || ok "no recovery admin on the server"
 
 echo