feat(backup): run pg_dump multiple times per day via BACKUP_TIMES_UTC

Replace the single BACKUP_HOUR/BACKUP_MINUTE slot with a comma-separated
list of UTC times. Scheduler walks all slots and sleeps until the soonest
future one, so four daily backups become a one-line env change:

    BACKUP_TIMES_UTC=02:30,08:30,14:30,20:30  (default)

Legacy BACKUP_HOUR/BACKUP_MINUTE still honored as a single slot for
backwards compatibility with existing .env files.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backup/entrypoint.sh

@@ -1,26 +1,62 @@
 #!/bin/sh
-# Loops forever: sleeps until the next BACKUP_HOUR:BACKUP_MINUTE UTC, then runs backup_db.sh.
-# Defaults: 02:30 UTC nightly.
+# Runs backup_db.sh at each time in BACKUP_TIMES_UTC (comma-separated HH:MM list).
+# Defaults: 02:30, 08:30, 14:30, 20:30 UTC — four backups per day.
+#
+# Back-compat: if BACKUP_TIMES_UTC is unset but legacy BACKUP_HOUR/BACKUP_MINUTE are,
+# those are honored as a single slot.
 
 set -eu
 
-HOUR="${BACKUP_HOUR:-2}"
-MINUTE="${BACKUP_MINUTE:-30}"
+if [ -n "${BACKUP_TIMES_UTC:-}" ]; then
+  TIMES="$BACKUP_TIMES_UTC"
+elif [ -n "${BACKUP_HOUR:-}" ] || [ -n "${BACKUP_MINUTE:-}" ]; then
+  TIMES="$(printf '%02d:%02d' "${BACKUP_HOUR:-2}" "${BACKUP_MINUTE:-30}")"
+else
+  TIMES="02:30,08:30,14:30,20:30"
+fi
+
+echo "[$(date -u +%FT%TZ)] backup schedule (UTC): ${TIMES}"
 
 if [ "${BACKUP_RUN_ON_START:-0}" = "1" ]; then
   echo "[$(date -u +%FT%TZ)] BACKUP_RUN_ON_START=1 — running backup immediately"
   /app/backup_db.sh || echo "[$(date -u +%FT%TZ)] initial backup failed (continuing)"
 fi
 
+# Compute epoch for "today HH:MM UTC" on both GNU and BSD date.
+slot_to_epoch_today() {
+  HM="$1"
+  date -u -d "today ${HM}:00" +%s 2>/dev/null \
+    || date -u -j -f "%H:%M:%S" "${HM}:00" +%s
+}
+
 while true; do
   NOW_EPOCH=$(date -u +%s)
-  TARGET=$(date -u -d "today ${HOUR}:${MINUTE}:00" +%s 2>/dev/null \
-           || date -u -j -f "%H:%M:%S" "${HOUR}:${MINUTE}:00" +%s)
-  if [ "$TARGET" -le "$NOW_EPOCH" ]; then
-    TARGET=$((TARGET + 86400))
+  NEXT=""
+  # Find the smallest TARGET > NOW across all configured slots (rolling to tomorrow if needed).
+  OLDIFS="$IFS"
+  IFS=','
+  for HM in $TIMES; do
+    HM="$(echo "$HM" | tr -d ' ')"
+    [ -z "$HM" ] && continue
+    T=$(slot_to_epoch_today "$HM")
+    if [ "$T" -le "$NOW_EPOCH" ]; then
+      T=$((T + 86400))
+    fi
+    if [ -z "$NEXT" ] || [ "$T" -lt "$NEXT" ]; then
+      NEXT="$T"
     fi
-  SLEEP=$((TARGET - NOW_EPOCH))
-  echo "[$(date -u +%FT%TZ)] next backup in ${SLEEP}s (at $(date -u -d "@${TARGET}" +%FT%TZ 2>/dev/null || date -u -r "${TARGET}" +%FT%TZ))"
-  sleep "$SLEEP"
-  /app/backup_db.sh || echo "[$(date -u +%FT%TZ)] backup failed (will retry tomorrow)"
+  done
+  IFS="$OLDIFS"
+
+  if [ -z "$NEXT" ]; then
+    echo "[$(date -u +%FT%TZ)] no valid times in BACKUP_TIMES_UTC='${TIMES}'; sleeping 1h"
+    sleep 3600
+    continue
+  fi
+
+  SLEEP=$((NEXT - NOW_EPOCH))
+  NEXT_ISO=$(date -u -d "@${NEXT}" +%FT%TZ 2>/dev/null || date -u -r "${NEXT}" +%FT%TZ)
+  echo "[$(date -u +%FT%TZ)] next backup in ${SLEEP}s (at ${NEXT_ISO})"
+  sleep "$SLEEP"
+  /app/backup_db.sh || echo "[$(date -u +%FT%TZ)] backup failed (will retry at next slot)"
 done

docker-compose.yaml

@@ -89,9 +89,9 @@ services:
         condition: service_healthy
     env_file: .env
     environment:
-      # Nightly pg_dump → rustfs. Credentials from .env (RUSTFS_*).
-      - BACKUP_HOUR=${BACKUP_HOUR:-2}
-      - BACKUP_MINUTE=${BACKUP_MINUTE:-30}
+      # pg_dump → rustfs. Credentials from .env (RUSTFS_*).
+      # BACKUP_TIMES_UTC: comma-separated HH:MM list. Default: 4×/day.
+      - BACKUP_TIMES_UTC=${BACKUP_TIMES_UTC:-02:30,08:30,14:30,20:30}
       - BACKUP_KEEP_DAYS=${BACKUP_KEEP_DAYS:-30}
       - BACKUP_RUN_ON_START=${BACKUP_RUN_ON_START:-0}
       - RUSTFS_ENDPOINT=${RUSTFS_ENDPOINT}