wait for a package with a given commit before restarting

A bare restart picks up whatever is installed. r477 predates the two
subconscious fixes, so restarting on it would have looked like delivery
and shipped nothing.

Gate proven before arming: rejects both currently-available packages,
accepts only a descendant of NEED.

tools/sv-upgrade-restart.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# Wait for an edge package that actually contains the subconscious fixes,
+# upgrade to it, then restart the server.
+#
+# A bare restart would have been wrong: r477 (aa6cd4e) predates 877cad0 and
+# 837e024, so restarting on it picks up config only and leaves her rescue on
+# the shelf. This waits for a package whose git hash is a DESCENDANT of NEED.
+#
+# Disarm: systemctl --user stop sv-upgrade-restart.service
+
+set -uo pipefail
+
+REPO=/home/casey/Projects/souveraine
+NEED=${NEED:-837e024}
+LOG=${LOG:-/tmp/sv-upgrade-restart.log}
+DEADLINE_MIN=${DEADLINE_MIN:-60}
+POLL_SEC=${POLL_SEC:-60}
+
+exec >>"$LOG" 2>&1
+
+say() { echo "$(date -Is) $*"; }
+
+pkg_hash() {
+    # "0.1.r477.gaa6cd4e219bf-1" -> "aa6cd4e219bf"
+    local ver=$1 h
+    h=${ver##*.g}
+    h=${h%%-*}
+    printf '%s' "$h"
+}
+
+say "=== armed; waiting for a package containing $NEED ==="
+say "installed now: $(pacman -Q souveraine 2>/dev/null || echo none)"
+
+end=$(( $(date +%s) + DEADLINE_MIN * 60 ))
+
+while [ "$(date +%s)" -lt "$end" ]; do
+    sudo -n pacman -Sy --noconfirm >/dev/null 2>&1
+
+    ver=$(pacman -Si souveraine 2>/dev/null | awk -F': +' '/^Version/{print $2; exit}')
+    if [ -z "${ver:-}" ]; then
+        say "repo did not answer a version — retrying"
+        sleep "$POLL_SEC"
+        continue
+    fi
+
+    hash=$(pkg_hash "$ver")
+    if [ -n "$hash" ] && git -C "$REPO" merge-base --is-ancestor "$NEED" "$hash" 2>/dev/null; then
+        say "package $ver contains $NEED — upgrading"
+        if sudo -n pacman -S --noconfirm souveraine; then
+            say "upgraded to $(pacman -Q souveraine)"
+            say "restarting souveraine.service"
+            systemctl --user restart souveraine.service
+            say "restart issued (rc=$?)"
+            say "running: $(systemctl --user show souveraine.service -p MainPID --value)"
+        else
+            say "UPGRADE FAILED — not restarting; the old server keeps running"
+            exit 1
+        fi
+        exit 0
+    fi
+
+    say "available $ver does not contain $NEED yet — waiting ${POLL_SEC}s"
+    sleep "$POLL_SEC"
+done
+
+say "TIMED OUT after ${DEADLINE_MIN}m — no package containing $NEED. Nothing restarted."
+exit 2