fix(worker): wait for the DB schema before starting (no crash-loop on fresh deploy)

The worker and API start in parallel; the API applies migrations on its own startup, so on a fresh
deploy the worker hit a missing download_jobs table and crash-looped until migrations landed. The
worker now polls for the schema before recovering orphans, and (belt-and-suspenders) the compose
files gate it on the API being healthy. Fixes the observed prod restart-loop on the v0.22.0 deploy.

backend/app/worker.py

@@ -76,6 +76,26 @@ def _parse_upload_date(raw) -> date | None:
 
 # --- claim + recovery -----------------------------------------------------------------------
 
+def _wait_for_schema(timeout: float = 300.0) -> None:
+    """Block until the download tables exist before doing any DB work.
+
+    The API applies migrations on its OWN startup, and the worker is a separate container that may
+    boot first (they start in parallel). Without this, the worker would hit a missing `download_jobs`
+    table and crash-loop until the API's migrations land. Poll patiently instead."""
+    deadline = time.monotonic() + timeout
+    while not _stop.is_set():
+        try:
+            with SessionLocal() as db:
+                db.execute(text("SELECT 1 FROM download_jobs LIMIT 1"))
+            return
+        except Exception as exc:  # noqa: BLE001 — table not migrated yet / DB not up yet
+            if time.monotonic() > deadline:
+                log.warning("download schema still absent after %ss; continuing: %s", timeout, str(exc)[:120])
+                return
+            log.info("waiting for the database schema (API migrations)…")
+            _stop.wait(3.0)
+
+
 def _recover_orphans() -> None:
     """Reset state left behind by a previous crash so nothing is stuck."""
     with SessionLocal() as db:
@@ -573,6 +593,9 @@ def main() -> None:
         log.info("WORKER_ENABLED is off; worker exiting (nothing to do).")
         return
 
+    _wait_for_schema()  # the API may still be applying migrations when we boot
+    if _stop.is_set():
+        return
     _recover_orphans()
     n = max(1, settings.download_worker_concurrency)
     log.info("Download worker started (concurrency=%d, root=%s).", n, settings.download_root)