Merge chore/code-hygiene: Phase 2 #4 Playlists (cleanup + bug fixes)

Cleanup (_remove_item dedup; drop dead Check import + plName shadow) plus
review-found bug fixes: reorder position-collision under concurrent edits,
push/sync/revert YouTube 403s now route to the Connect affordance, and
removeItem rolls back on failure. Verified: ruff, tsc, localdev boots healthy.

backend/app/routes/playlists.py

@@ -74,6 +74,23 @@ def _add_item(db: Session, pl: Playlist, video_id: str, *, mark_dirty: bool) ->
     return True
 
 
+def _remove_item(db: Session, pl: Playlist, video_id: str, *, mark_dirty: bool) -> bool:
+    """Remove a video from a playlist if present (idempotent). Returns whether it was removed.
+    `mark_dirty` recomputes the YouTube-sync dirty flag (skip for Watch later)."""
+    item = db.scalar(
+        select(PlaylistItem).where(
+            PlaylistItem.playlist_id == pl.id, PlaylistItem.video_id == video_id
+        )
+    )
+    if item is None:
+        return False
+    db.delete(item)
+    if mark_dirty:
+        recompute_dirty(db, pl)
+    db.commit()
+    return True
+
+
 def _summary(
     db: Session,
     pl: Playlist,
@@ -239,14 +256,7 @@ def remove_watch_later(
         )
     )
     if pl is not None:
-        item = db.scalar(
-            select(PlaylistItem).where(
-                PlaylistItem.playlist_id == pl.id, PlaylistItem.video_id == video_id
-            )
-        )
-        if item is not None:
-            db.delete(item)
-            db.commit()
+        _remove_item(db, pl, video_id, mark_dirty=False)
     return {"saved": False}
 
 
@@ -452,15 +462,7 @@ def remove_item(
     db: Session = Depends(get_db),
 ) -> dict:
     pl = _own_playlist(db, user, playlist_id)
-    item = db.scalar(
-        select(PlaylistItem).where(
-            PlaylistItem.playlist_id == pl.id, PlaylistItem.video_id == video_id
-        )
-    )
-    if item is not None:
-        db.delete(item)
-        recompute_dirty(db, pl)
-        db.commit()
+    _remove_item(db, pl, video_id, mark_dirty=True)
     return {"playlist_id": pl.id, "video_id": video_id}
 
 
@@ -480,11 +482,20 @@ def reorder_items(
         ).scalars()
     }
     pos = 0
+    seen: set[str] = set()
     for vid in order:
         it = items.get(vid)
         if it is not None:
             it.position = pos
             pos += 1
+            seen.add(vid)
+    # Any items the payload omitted (e.g. added concurrently in another tab) keep their relative
+    # order but get fresh trailing positions, so no two items collide on the same position.
+    for it in sorted(
+        (it for vid, it in items.items() if vid not in seen), key=lambda i: i.position
+    ):
+        it.position = pos
+        pos += 1
     recompute_dirty(db, pl)
     db.commit()
     return {"playlist_id": pl.id, "count": pos}

frontend/src/components/Playlists.tsx

@@ -19,7 +19,6 @@ import { CSS } from "@dnd-kit/utilities";
 import {
   ArrowDown,
   ArrowUp,
-  Check,
   ExternalLink,
   GripVertical,
   ListPlus,
@@ -37,6 +36,7 @@ import {
 import { api, type Playlist, type Video } from "../lib/api";
 import { formatDuration } from "../lib/format";
 import { notify } from "../lib/notifications";
+import { notifyYouTubeActionError } from "../lib/youtubeErrors";
 import { getAccountRaw, LS, readAccountMerged, setAccountRaw, writeAccount } from "../lib/storage";
 import { useUndoable } from "../lib/useUndoable";
 const PlayerModal = lazy(() => import("./PlayerModal"));
@@ -347,14 +347,13 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
       danger: true,
     });
     if (!ok) return;
-    const plName = detail.kind === "watch_later" ? t("playlists.watchLater") : detail.name;
     setReverting(true);
     try {
       await api.revertPlaylist(selectedId);
       refreshAll();
-      notify({ level: "success", message: t("playlists.revertDone", { name: plName }) });
-    } catch {
-      notify({ level: "warning", message: t("playlists.revertFailed") });
+      notify({ level: "success", message: t("playlists.revertDone", { name: plName(detail) }) });
+    } catch (e) {
+      notifyYouTubeActionError(e, t("playlists.revertFailed"));
     } finally {
       setReverting(false);
     }
@@ -362,12 +361,11 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
 
   async function pushToYoutube() {
     if (selectedId == null || !detail || pushing) return;
-    const plName = detail.kind === "watch_later" ? t("playlists.watchLater") : detail.name;
     setPushing(true);
     try {
       const plan = await api.playlistPushPlan(selectedId);
       if (plan.action === "update" && !plan.to_insert && !plan.to_delete && !plan.to_reorder) {
-        notify({ level: "info", message: t("playlists.pushUpToDate", { name: plName }) });
+        notify({ level: "info", message: t("playlists.pushUpToDate", { name: plName(detail) }) });
         return;
       }
       if (!plan.affordable) {
@@ -406,10 +404,10 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
       if (r.failures.length) {
         notify({ level: "warning", message: t("playlists.pushPartial", { count: r.failures.length }) });
       } else {
-        notify({ level: "success", message: t("playlists.pushDone", { name: plName }) });
+        notify({ level: "success", message: t("playlists.pushDone", { name: plName(detail) }) });
       }
-    } catch {
-      notify({ level: "warning", message: t("playlists.pushFailed") });
+    } catch (e) {
+      notifyYouTubeActionError(e, t("playlists.pushFailed"));
     } finally {
       setPushing(false);
     }
@@ -423,8 +421,8 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
       qc.invalidateQueries({ queryKey: ["playlists"] });
       qc.invalidateQueries({ queryKey: ["playlist"] });
       notify({ level: "success", message: t("playlists.syncedToast", { count: r.synced }) });
-    } catch {
-      notify({ level: "warning", message: t("playlists.syncFailed") });
+    } catch (e) {
+      notifyYouTubeActionError(e, t("playlists.syncFailed"));
     } finally {
       setSyncing(false);
     }
@@ -463,8 +461,14 @@ export default function Playlists({ canWrite }: { canWrite: boolean }) {
     const next = items.filter((v) => v.id !== videoId);
     order.reset(next);
     lastSetRef.current = idsKey(next);
-    await api.removeFromPlaylist(selectedId, videoId);
-    refreshAll();
+    try {
+      await api.removeFromPlaylist(selectedId, videoId);
+      refreshAll();
+    } catch {
+      // The optimistic removal above didn't stick — resync from the server to restore the row.
+      // api.req already surfaced the error to the user via the global error dialog.
+      refreshAll();
+    }
   }
 
   async function saveRename() {