feat(backend): wire playlist upsert in SyncService before scanning;

publish events and persist DB on rename/delete/download;
worker: retry failed downloads with simple backoff;
add compute/apply CLI with per-playlist summary;
record last_sync after applying actions

src/app/cli.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+import argparse
+import asyncio
+from pathlib import Path
+
+from .config.settings import Settings
+from .core.database.db import Database
+from .core.sync.service import SyncService
+from .core.sync.executor import ActionExecutor
+from .core.events.event_bus import EventBus
+from .core.utils.yt import extract_playlist_id
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description="YouTube Playlist Sync — compute/apply actions")
+    parser.add_argument("--apply", action="store_true", help="Apply actions (otherwise compute-only)")
+    parser.add_argument("--db", type=Path, default=Path("app/data/app.db"), help="Path to SQLite database")
+    parser.add_argument("--playlist", type=int, default=None, help="Only run for a specific playlist index (0-based)")
+    args = parser.parse_args(argv)
+
+    settings = Settings()
+    db = Database(args.db.resolve())
+    service = SyncService(db)
+    bus = EventBus()
+    executor = ActionExecutor(db, event_bus=bus)
+
+    async def log_event(payload):
+        # Placeholder subscriber for future GUI/log integration
+        print(f"EVENT: {payload}")
+
+    # Subscribe to key events
+    bus.subscribe("DownloadStarted", log_event)
+    bus.subscribe("DownloadCompleted", log_event)
+    bus.subscribe("DownloadFailed", log_event)
+    bus.subscribe("RenameApplied", log_event)
+    bus.subscribe("FileRecycled", log_event)
+
+    playlists = settings.playlists
+    if args.playlist is not None:
+        playlists = [playlists[args.playlist]] if 0 <= args.playlist < len(playlists) else []
+
+    for pl in playlists:
+        url = pl.get("url")
+        pid = extract_playlist_id(url) or (url or "")
+        actions = service.sync_from_config(pl)
+        counts: dict[str, int] = {}
+        for a in actions:
+            counts[a.type.name] = counts.get(a.type.name, 0) + 1
+        summary = ", ".join(f"{k}:{v}" for k, v in sorted(counts.items()))
+        print(f"Playlist {pid}: {len(actions)} actions → {summary}")
+        if args.apply and actions:
+            asyncio.run(executor.execute(actions, pl))
+            db.set_playlist_last_sync(pid)
+            print(f"Applied actions for {pid}.")
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())