fix(youtube): "this playlist no longer exists" only where the user picked that list

playlistNotFound was mapped to "gone" everywhere: exploring a channel without uploads (its
uploads list answers not found) and a list deleted mid bulk pull both said a playlist no
longer exists. The reason is now "gone" only on single-playlist routes; explore reads it
as an empty back-catalogue, and the bulk pull skips that list and syncs the rest.

backend/app/routes/_common.py

@@ -60,14 +60,17 @@ def owned_or_404(
     return obj
 
 
-def youtube_refusal(exc: Exception) -> HTTPException:
+def youtube_refusal(exc: Exception, *, playlist: bool = False) -> HTTPException:
     """The answer to an action YouTube refused: a 422 whose reason the UI translates
     (`errors.youtube.<reason>`). One definition, because the routes had grown three shapes of it —
     a bare English string quoting the upstream message, a playlist-scoped reason, and nothing at
     all (a raw 500 from the manual syncs). The upstream failure is already logged where it
     happened (`youtube.api.error`). A failure that is not the Data API's (the search scraper's) is
-    YouTube being unavailable to us — the retryable answer."""
-    reason = refusal_reason(exc) if isinstance(exc, YouTubeError) else "unavailable"
+    YouTube being unavailable to us — the retryable answer. `playlist`: the route acts on one
+    playlist the user picked, so a missing playlist is THAT one, gone (`refusal_reason`)."""
+    reason = (
+        refusal_reason(exc, playlist=playlist) if isinstance(exc, YouTubeError) else "unavailable"
+    )
     return HTTPException(status_code=422, detail={"code": "youtube", "reason": reason})
 
 

backend/app/routes/playlists.py

@@ -372,7 +372,7 @@ def revert_youtube(
             raise not_found("playlist") from None
         except YouTubeError as exc:
             db.rollback()
-            raise youtube_refusal(exc) from exc
+            raise youtube_refusal(exc, playlist=True) from exc
 
 
 def _pushable(db: Session, user: User, playlist_id: int) -> Playlist:
@@ -398,7 +398,7 @@ def push_plan(
         with quota.attribute(user.id, quota.QuotaAction.PLAYLISTS_PUSH):
             plan = plan_merge(db, user, pl)
     except YouTubeError as exc:
-        raise youtube_refusal(exc) from exc
+        raise youtube_refusal(exc, playlist=True) from exc
     plan["remaining_today"] = quota.remaining_today(db)
     plan["affordable"] = plan["units_estimate"] <= plan["remaining_today"]
     return plan
@@ -439,7 +439,7 @@ def push(
             raise not_found("playlist") from None
         except YouTubeError as exc:
             db.rollback()
-            raise youtube_refusal(exc) from exc
+            raise youtube_refusal(exc, playlist=True) from exc
 
 
 @router.get("/{playlist_id}")
@@ -539,7 +539,7 @@ def delete_playlist(
                     with YouTubeClient(db, user) as yt:
                         yt.delete_playlist(pl.yt_playlist_id)
             except YouTubeError as exc:
-                raise youtube_refusal(exc) from exc
+                raise youtube_refusal(exc, playlist=True) from exc
         # The playlist first, as every item write: the cascade deletes the items before the list row.
         lock_playlists(db, pl.id)
         db.delete(pl)  # items cascade