Add daily timezone drift check

tz-drift-check.sh + sky-cam-tzcheck timer notify when TIMEZONE no longer
matches the machine's timezone (timers follow the machine, scripts follow TIMEZONE).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013wi3ZRpfenCe2TRwT4JFMG

install.sh

@@ -296,6 +296,25 @@ for cam in "${CAMERAS[@]}"; do
     fi
 done
 
+# ── Timezone drift check ─────────────────────────────────────────────────────
+# Daily + shortly after boot: notify if TIMEZONE no longer matches the
+# machine's timezone (systemd timers follow the machine, scripts follow TIMEZONE).
+write_service "sky-cam-tzcheck" "timezone drift check" "tz-drift-check.sh"
+cat > "$UNIT_DIR/sky-cam-tzcheck.timer" <<EOF2
+[Unit]
+Description=Sky-Cam — timezone drift check
+
+[Timer]
+OnBootSec=3min
+OnCalendar=*-*-* 12:00:00
+Persistent=true
+
+[Install]
+WantedBy=timers.target
+EOF2
+echo "  wrote sky-cam-tzcheck.timer"
+timers+=("sky-cam-tzcheck")
+
 # ── Generate .env.example ────────────────────────────────────────────────────
 env_example="$HERE/.env.example"
 {

tz-drift-check.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+# tz-drift-check.sh — warn if TIMEZONE (sky-cam.conf / .env) no longer matches
+# the machine's own timezone.
+#
+# systemd timers fire on the machine's clock, but sunrise.py, the capture
+# scripts and the per-day folder names use TIMEZONE. If the two drift apart
+# (someone ran `timedatectl set-timezone`, a cloud-init reset, a restored
+# image, a typo in .env...) every scheduled job runs at the wrong local time
+# and the sunrise capture window is off by the zone difference.
+#
+# Run daily by sky-cam-tzcheck.timer (and shortly after boot). Sends one
+# notify.sh message per run while the mismatch persists; silent when fine.
+# Exit 0 either way — a mismatch is a notification, not a job failure.
+
+set -uo pipefail
+
+SCRIPT_DIR="$(dirname "$(realpath "$0")")"
+source "$SCRIPT_DIR/sky-cam.conf"
+source "$SCRIPT_DIR/.env" 2>/dev/null || true
+
+# Machine's zone — read WITHOUT any TZ override so we see the real system value.
+sys_tz="$(env -u TZ timedatectl show -p Timezone --value 2>/dev/null)"
+[ -z "$sys_tz" ] && sys_tz="$(cat /etc/timezone 2>/dev/null)"
+[ -z "$sys_tz" ] && sys_tz="$(readlink /etc/localtime 2>/dev/null | sed 's|.*/zoneinfo/||')"
+if [ -z "$sys_tz" ]; then
+    echo "tz-drift-check: could not determine the machine's timezone — skipping"
+    exit 0
+fi
+
+# Compare by real UTC offsets across the year so aliases (US/Eastern vs
+# America/New_York) and identical-rule zones are not reported as drift.
+same=true
+if [ "$sys_tz" != "$TIMEZONE" ]; then
+    for m in 01 04 07 10; do
+        a="$(TZ="$sys_tz"   date -d "2026-$m-15 12:00 UTC" +%z)"
+        b="$(TZ="$TIMEZONE" date -d "2026-$m-15 12:00 UTC" +%z)"
+        [ "$a" = "$b" ] || { same=false; break; }
+    done
+fi
+
+if $same; then
+    echo "Timezone OK: sky-cam TIMEZONE=$TIMEZONE, machine=$sys_tz"
+    exit 0
+fi
+
+msg="sky-cam TIMEZONE is $TIMEZONE but this machine's timezone is $sys_tz. Scheduled jobs run on the machine clock, so sunrise/seasons/moon jobs will fire at the wrong local time. Fix: set TIMEZONE=$sys_tz in $SCRIPT_DIR/.env and re-run ./install.sh, or run: sudo timedatectl set-timezone $TIMEZONE"
+echo "WARNING: $msg"
+"$SCRIPT_DIR/notify.sh" "WARNING: sky-cam timezone mismatch" "$msg" || true
+exit 0