chore: structured timestamped logging across the backend

- uvicorn --log-config (log_config.json): timestamped formatters for uvicorn
  access/error and the app's own "subfeed" loggers (ms precision)
- Log key activity: startup/shutdown, login/denied, token refresh, YouTube API
  errors, subscription imports, sync pause/resume
- Background sync jobs no longer swallow errors silently — failures in RSS poll,
  backfill, enrichment, autotag and resync are logged with tracebacks

backend/app/sync/autotag.py

@@ -5,11 +5,14 @@ detection over a sample of recent video titles. Topics are mapped from YouTube's
 topicDetails categories and the channel's dominant video category. System tags are
 regenerated freely; user tags are never touched here.
 """
+import logging
 import re
 
 from sqlalchemy import and_, exists, func, select
 from sqlalchemy.orm import Session
 
+log = logging.getLogger("subfeed.autotag")
+
 from app.config import settings
 from app.models import Channel, ChannelTag, Tag, Video
 
@@ -273,6 +276,7 @@ def run_autotag_all(db: Session, only_missing: bool = False) -> dict:
             tagged += 1
         except Exception:
             db.rollback()
+            log.exception("Auto-tagging failed for channel %s", channel.id)
     removed = _cleanup_orphan_system_tags(db)
     return {"channels_tagged": tagged, "orphan_tags_removed": removed}
 

backend/app/sync/runner.py

@@ -4,11 +4,15 @@ Channel/video data is shared across users, so background work acts through a "se
 user" (any user with a stored refresh token) unless a YOUTUBE_API_KEY is configured for
 public reads.
 """
+import logging
+
 from sqlalchemy import select
 from sqlalchemy.orm import Session
 
 from app import quota
 from app.config import settings
+
+log = logging.getLogger("subfeed.sync")
 from app.models import Channel, OAuthToken, User
 from app.sync.subscriptions import import_subscriptions
 from app.sync.videos import (
@@ -43,6 +47,7 @@ def run_rss_poll(db: Session, channels: list[Channel] | None = None) -> int:
             new += poll_rss_channel(db, channel)
         except Exception:
             db.rollback()
+            log.exception("RSS poll failed for channel %s", channel.id)
     return new
 
 
@@ -83,6 +88,7 @@ def run_subscription_resync(db: Session) -> dict:
             import_subscriptions(db, user)
         except Exception:
             db.rollback()
+            log.exception("Subscription resync failed for user %s", user.id)
     return {"users": len(users)}
 
 
@@ -111,6 +117,7 @@ def run_recent_backfill(
                 processed += 1
             except Exception:
                 db.rollback()
+                log.exception("Recent backfill failed for channel %s", channel.id)
     return {"channels_processed": processed, "videos_added": videos_added}
 
 
@@ -139,4 +146,5 @@ def run_deep_backfill(db: Session, max_channels: int = 10, max_pages: int = 5) -
                 processed += 1
             except Exception:
                 db.rollback()
+                log.exception("Deep backfill failed for channel %s", channel.id)
     return {"channels_processed": processed, "videos_added": videos_added}

backend/app/sync/subscriptions.py

@@ -1,4 +1,5 @@
 """Import the authenticated user's YouTube subscriptions and channel metadata."""
+import logging
 from datetime import datetime, timezone
 
 from sqlalchemy import select
@@ -7,6 +8,8 @@ from sqlalchemy.orm import Session
 from app.models import Channel, Subscription, User
 from app.youtube.client import YouTubeClient, best_thumbnail
 
+log = logging.getLogger("subfeed.sync")
+
 
 def _to_int(value) -> int | None:
     try:
@@ -107,9 +110,11 @@ def import_subscriptions(db: Session, user: User) -> dict:
             detailed = len(items)
         db.commit()
 
-    return {
+    result = {
         "subscriptions": len(fetched),
         "channels_new": new_channels,
         "channels_detailed": detailed,
         "removed_stale": removed,
     }
+    log.info("Subscription import (user %s): %s", user.id, result)
+    return result