Run post-backup pruning through SQL retention

Stop passing prune options into the legacy scheduled backup engine from the
Django backup command. Record the completed snapshot first, then apply retention
through the SQL-backed retention service so pruning sees the same SnapshotRecord
state as the admin and retention command.

Also record prune failures on BackupRun.result instead of leaving the run in an
ambiguous state.

src/pobsync_backend/management/commands/run_pobsync_backup.py

@@ -11,6 +11,7 @@ from pobsync.commands.run_scheduled import run_scheduled
 from pobsync.paths import PobsyncPaths
 from pobsync_backend.config_source import DjangoConfigSource
 from pobsync_backend.models import BackupRun, HostConfig
+from pobsync_backend.retention import run_sql_retention_apply
 from pobsync_backend.snapshot_discovery import infer_snapshot_kind, upsert_snapshot_record
 
 
@@ -45,9 +46,7 @@ class Command(BaseCommand):
                 prefix=paths.home,
                 host=host.host,
                 dry_run=bool(options["dry_run"]),
-                prune=bool(options["prune"]),
-                prune_max_delete=int(options["prune_max_delete"]),
-                prune_protect_bases=bool(options["prune_protect_bases"]),
+                prune=False,
                 config_source=DjangoConfigSource(),
             )
         except Exception as exc:
@@ -72,7 +71,38 @@ class Command(BaseCommand):
                 snapshot_record, _created = upsert_snapshot_record(host=host, kind=kind, snapshot_dir=snapshot_path)
             except ValueError:
                 snapshot_record = None
+
+        if result.get("ok") and not result.get("dry_run") and options["prune"]:
+            try:
+                result["prune"] = run_sql_retention_apply(
+                    prefix=paths.home,
+                    host=host.host,
+                    kind="scheduled",
+                    protect_bases=bool(options["prune_protect_bases"]),
+                    yes=True,
+                    max_delete=int(options["prune_max_delete"]),
+                    acquire_lock=False,
+                )
+            except Exception as exc:
+                result["prune"] = {"ok": False, "error": str(exc), "type": type(exc).__name__}
+                run.status = BackupRun.Status.FAILED
+                run.result = result
+                run.snapshot = snapshot_record
+                run.save(
+                    update_fields=[
+                        "status",
+                        "ended_at",
+                        "snapshot_path",
+                        "snapshot",
+                        "base_path",
+                        "rsync_exit_code",
+                        "result",
+                    ],
+                )
+                raise
+
         run.snapshot = snapshot_record
+        run.result = result
         run.save(
             update_fields=[
                 "status",