fix(worker): survive startup race — wrap poll in try/except, add restart policy and backend healthcheck dependency

- Poll loop body is now wrapped in outer try/except so UndefinedTable (or any
  transient DB error) logs a warning and retries after poll_interval instead of
  killing the worker process.
- docker-compose: worker gets `restart: unless-stopped` so Docker recovers it
  automatically on any unexpected exit.
- docker-compose: worker `depends_on` now includes `backend: condition: service_healthy`
  so it waits for the backend (which runs migrations) to be ready before polling.

Fixes DAP-40.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -38,6 +38,7 @@ services:
 
   worker:
     build: ./worker
+    restart: unless-stopped
     environment:
       DATABASE_URL: postgresql://kino:${DB_PASSWORD:-kino}@db:5432/kino
       MEDIA_PATH: /media
@@ -48,6 +49,8 @@ services:
     depends_on:
       db:
         condition: service_healthy
+      backend:
+        condition: service_healthy
 
   frontend:
     build: ./frontend

worker/src/worker.py

@@ -86,18 +86,22 @@ def process_job(db: Session, dl: Download) -> None:
 def run() -> None:
     log.info("Worker started, polling every %ds", settings.poll_interval)
     while True:
-        with Session(engine) as db:
-            pending = db.execute(
-                select(Download).where(Download.status == DownloadStatus.pending).limit(1)
-            ).scalar_one_or_none()
-            if pending:
-                try:
-                    process_job(db, pending)
-                except Exception as exc:
-                    log.error("Job %d failed: %s", pending.id, exc)
-                    pending.status = DownloadStatus.failed
-                    pending.error = str(exc)
-                    db.commit()
+        try:
+            with Session(engine) as db:
+                pending = db.execute(
+                    select(Download).where(Download.status == DownloadStatus.pending).limit(1)
+                ).scalar_one_or_none()
+                if pending:
+                    try:
+                        process_job(db, pending)
+                    except Exception as exc:
+                        log.error("Job %d failed: %s", pending.id, exc)
+                        pending.status = DownloadStatus.failed
+                        pending.error = str(exc)
+                        db.commit()
+        except Exception as exc:
+            # Transient errors (e.g. table not yet created, DB not ready) — backoff and retry
+            log.warning("Poll error (will retry): %s", exc)
         time.sleep(settings.poll_interval)