feat: make Django configs drive backups and scheduling

Treat SQL-backed Django models as the source of truth for pobsync
configuration, exporting runtime YAML only as a compatibility layer for
the existing engine. Add a database-driven scheduler command, Docker
scheduler services, schedule run-state fields, and tests for scheduler,
config export, and retention behavior.

src/pobsync_backend/management/commands/run_pobsync_scheduler.py

@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+import time
+from pathlib import Path
+from typing import Any
+
+from django.conf import settings
+from django.core.management import call_command
+from django.core.management.base import BaseCommand
+from django.db import transaction
+from django.utils import timezone
+
+from pobsync_backend.models import ScheduleConfig
+from pobsync_backend.scheduler import due_key, is_due
+
+
+class Command(BaseCommand):
+    help = "Run due pobsync schedules from the Django database."
+
+    def add_arguments(self, parser) -> None:
+        parser.add_argument("--prefix", default=settings.POBSYNC_HOME, help="Pobsync home directory")
+        parser.add_argument("--once", action="store_true", help="Check once and exit")
+        parser.add_argument("--loop", action="store_true", help="Keep checking schedules")
+        parser.add_argument("--interval", type=int, default=60, help="Loop interval in seconds")
+        parser.add_argument("--dry-run", action="store_true", help="Pass --dry-run to backup runs")
+
+    def handle(self, *args: Any, **options: Any) -> None:
+        if not options["once"] and not options["loop"]:
+            options["once"] = True
+
+        prefix = Path(options["prefix"])
+        while True:
+            count = self._run_due(prefix=prefix, dry_run=bool(options["dry_run"]))
+            self.stdout.write(f"Ran {count} due schedule(s).")
+            if options["once"]:
+                return
+            time.sleep(max(1, int(options["interval"])))
+
+    def _run_due(self, *, prefix: Path, dry_run: bool) -> int:
+        now = timezone.localtime(timezone.now())
+        current_due_key = due_key(now)
+        ran = 0
+
+        schedules = (
+            ScheduleConfig.objects.select_related("host")
+            .filter(enabled=True, host__enabled=True)
+            .order_by("host__host")
+        )
+        for schedule in schedules:
+            if schedule.last_due_key == current_due_key:
+                continue
+            if not is_due(schedule.cron_expr, now):
+                continue
+
+            with transaction.atomic():
+                locked = ScheduleConfig.objects.select_for_update().get(pk=schedule.pk)
+                if locked.last_due_key == current_due_key:
+                    continue
+                locked.last_due_key = current_due_key
+                locked.last_started_at = timezone.now()
+                locked.last_status = "running"
+                locked.save(update_fields=["last_due_key", "last_started_at", "last_status", "updated_at"])
+
+            status = "success"
+            try:
+                call_command(
+                    "run_pobsync_backup",
+                    schedule.host.host,
+                    prefix=str(prefix),
+                    dry_run=dry_run,
+                    prune=schedule.prune,
+                    prune_max_delete=schedule.prune_max_delete,
+                    prune_protect_bases=schedule.prune_protect_bases,
+                )
+            except Exception as exc:
+                status = "failed"
+                self.stderr.write(f"{schedule.host.host}: {type(exc).__name__}: {exc}")
+            finally:
+                ScheduleConfig.objects.filter(pk=schedule.pk).update(
+                    last_finished_at=timezone.now(),
+                    last_status=status,
+                )
+            ran += 1
+
+        return ran