fix(ui): a write that fails says what failed and why, wherever it fails

`req` opens its blocking dialog for 400/409/422/5xx only. A 403/404/429 was left to the caller and a
502-504 or lost connection got just the self-clearing connection notice, so 34 mutations without a
reporting onError and 15 direct api writes with a bare or missing catch failed in silence: a hidden
channel that snapped back, a share link that never revoked, a confirmed account delete that ended
with nothing said.

- lib/queryClient: one MutationCache reporter. react-query awaits it BEFORE the mutation's own
  onError, so it waits a task and skips a failure the site already reported; the toast title comes
  from `meta.failTitle`, `meta.errorShownInline` opts out.
- notifyActionError: title names WHAT failed, the line under it says WHY (`failureReason`: a
  structured localized detail, else the status). It marks the error reported (`markReported`), so
  nothing reports one failure twice; `notifyKnownFailure` for a site's own specific sentence.
- Every silent site named (45 new HU/EN titles, 4 reasons). Stale "the global dialog shows it"
  comments corrected on the job actions, channel block, Plex sync, cookies, download enqueue,
  account delete and usePref.
- Channels passed the tag hook's channel id to the reporter as the error; the tag and priority hooks
  now report themselves, with the real error.
- A contract test keeps every useMutation naming its failure; CLAUDE.md gains the pattern row.
- history.dom.test: the "navigates only once the entries are back" assertion raced an async act's
  macrotask flush (1 in 5 runs); it now asserts from a later popstate listener.

frontend/src/components/AccountPanel.tsx

@@ -7,6 +7,7 @@ import { LoadingState, StateMessage } from "./ui/QueryState";
 import { api } from "../lib/api";
 import { qk } from "../lib/queryKeys";
 import { notify } from "../lib/notifications";
+import { notifyActionError, notifyKnownFailure } from "../lib/actionErrors";
 import { copyText } from "../lib/clipboard";
 import { invalidateUserAccess, isEmailOff } from "../lib/adminUsers";
 import type { AdminUserAccess, AdminUserRow } from "../lib/api/admin";
@@ -66,25 +67,22 @@ export default function AccountPanel({
   const issue = useMutation({
     mutationFn: () => api.createSetPasswordLink(user.id),
     onSuccess: (r) => setLink({ url: r.url, expires_at: r.expires_at }),
-    onError: () => notify({ level: "error", message: t("users.account.linkFailed") }),
+    onError: (err) => notifyActionError(err, t("users.account.linkFailed")),
   });
 
   const resend = useMutation({
     mutationFn: () => api.resendUserVerification(user.id),
     onSuccess: () => notify({ level: "success", message: t("users.account.resendSent") }),
     onError: (err) =>
-      notify({
-        level: "error",
-        message: isEmailOff(err)
-          ? t("users.pendingAccess.resendEmailOff")
-          : t("users.pendingAccess.resendFailed"),
-      }),
+      isEmailOff(err)
+        ? notifyKnownFailure(err, t("users.pendingAccess.resendEmailOff"))
+        : notifyActionError(err, t("users.pendingAccess.resendFailed")),
   });
 
   const activate = useMutation({
     mutationFn: () => api.activateUser(user.id),
     onSuccess: () => invalidateUserAccess(qc, user.id),
-    onError: () => notify({ level: "error", message: t("users.pendingAccess.activateFailed") }),
+    onError: (err) => notifyActionError(err, t("users.pendingAccess.activateFailed")),
   });
 
   const copy = async () => {

frontend/src/components/AdminUsers.dom.test.tsx

@@ -86,7 +86,8 @@ describe("a user action that fails", () => {
     await waitFor(() =>
       expect(notify).toHaveBeenCalledWith({
         level: "error",
-        message: i18n.t("errors.notFound.user"), // the request layer localizes a structured detail
+        title: "users.roles.failed", // what failed…
+        message: i18n.t("errors.notFound.user"), // …and why: the request layer localizes a structured detail
       }),
     );
     await waitFor(() => expect(users).toHaveBeenCalledTimes(2));

frontend/src/components/AdminUsers.tsx

@@ -38,7 +38,7 @@ import { useConfirm } from "./ConfirmProvider";
 import Tabs, { usePersistedTab } from "./ui/Tabs";
 import { PageToolbar } from "./ui/PageShell";
 import { useMe } from "../lib/useMe";
-import { notifyActionError } from "../lib/actionErrors";
+import { notifyActionError, notifyKnownFailure } from "../lib/actionErrors";
 
 // Admin-only user & access management: roles, access requests (the Invite whitelist), and the
 // demo whitelist + reset. Each section is its own tab (persisted across reloads); the Access tab
@@ -351,7 +351,7 @@ function PendingAccess() {
       refresh();
       notify({ level: "success", message: t("users.pendingAccess.activated", { email: u.email }) });
     },
-    onError: () => notify({ level: "error", message: t("users.pendingAccess.activateFailed") }),
+    onError: (err) => notifyActionError(err, t("users.pendingAccess.activateFailed")),
   });
 
   const resend = useMutation({
@@ -363,12 +363,9 @@ function PendingAccess() {
     // The public resend is deliberately silent; this one is not, so say WHY it failed — an instance
     // with no working SMTP would otherwise show a success toast for a mail that was never sent.
     onError: (err) =>
-      notify({
-        level: "error",
-        message: isEmailOff(err)
-          ? t("users.pendingAccess.resendEmailOff")
-          : t("users.pendingAccess.resendFailed"),
-      }),
+      isEmailOff(err)
+        ? notifyKnownFailure(err, t("users.pendingAccess.resendEmailOff"))
+        : notifyActionError(err, t("users.pendingAccess.resendFailed")),
   });
 
   const list = rows.data ?? [];
@@ -563,12 +560,8 @@ function AdminInvites() {
       // A 409 means the list was stale — someone registered on that address since it loaded. Say
       // what to do instead of a generic failure, and refetch so the row re-renders as read-only.
       const conflict = e instanceof HttpError && e.status === 409;
-      notify({
-        level: "error",
-        message: t(
-          conflict ? "settings.invites.deleteHasAccount" : "settings.invites.deleteFailed",
-        ),
-      });
+      if (conflict) notifyKnownFailure(e, t("settings.invites.deleteHasAccount"));
+      else notifyActionError(e, t("settings.invites.deleteFailed"));
       if (conflict) refresh();
     },
   });
@@ -599,13 +592,9 @@ function AdminInvites() {
       notify({ level: "success", message: t("settings.invites.invited", { email: v.inv.email }) });
     },
     onError: (err) =>
-      notify({
-        level: "error",
-        message:
-          err instanceof HttpError && inviteEmailOff(err)
-            ? t("settings.invites.inviteEmailOff")
-            : t("settings.invites.inviteFailed"),
-      }),
+      err instanceof HttpError && inviteEmailOff(err)
+        ? notifyKnownFailure(err, t("settings.invites.inviteEmailOff"))
+        : notifyActionError(err, t("settings.invites.inviteFailed")),
   });
   // The one recipient the app has no language signal about: the admin typed this address in, so
   // nobody ever told us how to write to its owner. The dialog is where that gets decided — and it

frontend/src/components/ChannelPage.tsx

@@ -29,6 +29,7 @@ import { useFeedFilters } from "./FeedFiltersProvider";
 import { useConfirm } from "./ConfirmProvider";
 import { notify } from "../lib/notifications";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
+import { notifyActionError } from "../lib/actionErrors";
 import { api, DEFAULT_TAG_MODES, type FeedFilters, type Me, type ChannelDetail } from "../lib/api";
 import type { FeedView } from "../lib/feedView";
 import { channelYouTubeUrl, formatViews } from "../lib/format";
@@ -106,18 +107,23 @@ export default function ChannelPage({
   const runExplore = useCallback(
     (token?: string | null) => {
       setExploring(true);
-      return api
-        .exploreChannel(channelId, token ?? undefined)
-        .then((r) => {
-          setNextToken(r.next_page_token);
-          qc.invalidateQueries({ queryKey: qk.feed() });
-          // Refetch the detail so `explored` flips true → the "Exploring" badge shows on the
-          // first visit (the GET that drove this render predated the explore that just ran).
-          qc.invalidateQueries({ queryKey: qk.channel(channelId) });
-        })
-        .finally(() => setExploring(false));
+      return (
+        api
+          .exploreChannel(channelId, token ?? undefined)
+          .then((r) => {
+            setNextToken(r.next_page_token);
+            qc.invalidateQueries({ queryKey: qk.feed() });
+            // Refetch the detail so `explored` flips true → the "Exploring" badge shows on the
+            // first visit (the GET that drove this render predated the explore that just ran).
+            qc.invalidateQueries({ queryKey: qk.channel(channelId) });
+          })
+          // Both the automatic first-visit explore and "load more" used to fail in silence: an empty
+          // channel page that looked like a channel with no videos (E11 S2b).
+          .catch((err: unknown) => notifyActionError(err, t("errors.writeFailed.exploreChannel")))
+          .finally(() => setExploring(false))
+      );
     },
-    [channelId, qc],
+    [channelId, qc, t],
   );
 
   // First visit of an un-subscribed channel → ingest its recent uploads. Skipped for the demo
@@ -129,7 +135,7 @@ export default function ChannelPage({
     if (ch.subscribed || ch.blocked) return;
     if (ch.explored && ch.stored_videos > 0) return;
     autoTried.current = channelId;
-    runExplore().catch(() => {});
+    void runExplore();
   }, [ch, channelId, me.is_demo, runExplore]);
 
   const block = useMutation({
@@ -139,15 +145,16 @@ export default function ChannelPage({
       qc.invalidateQueries({ queryKey: qk.feed() });
       qc.invalidateQueries({ queryKey: qk.blockedChannels() });
     },
-    // No onError: block/unblock is a local DB op (not a YouTube write, so no 403 "connect" case),
-    // and its 400/409/422/500 are already surfaced by the global error modal (see api.ts req) —
-    // a caller toast here would just double it.
+    // No onError: a local DB op (not a YouTube write, so no 403 "connect" case). The app-wide
+    // reporter names the failure the error dialog does not cover (a 404 for a channel gone).
+    meta: { failTitle: "errors.writeFailed.blockChannel" },
   });
 
   // "Hide from feed": the same per-subscription flag the manager toggles (updateChannel {hidden}).
   // Local DB op — keeps the subscription, only drops the channel's videos from the feed/explore.
   const toggleHidden = useMutation({
     mutationFn: () => api.updateChannel(channelId, { hidden: !ch?.hidden }),
+    meta: { failTitle: "errors.writeFailed.hideChannel" },
     onSuccess: () => {
       qc.invalidateQueries({ queryKey: qk.channel(channelId) });
       qc.invalidateQueries({ queryKey: qk.feed() });

frontend/src/components/Channels.tsx

@@ -6,7 +6,6 @@ import { Ban, Eye, EyeOff, History, LayoutGrid, Pencil, RefreshCw, Table, X } fr
 import ExcludedChannelList from "./ExcludedChannelList";
 import { api, NO_TAG_SENTINEL, type ManagedChannel } from "../lib/api";
 import { Sparkles } from "lucide-react";
-import { notifyActionError } from "../lib/actionErrors";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
 import { accountKey, LS } from "../lib/storage";
 import { buildChannelColumns, applySyncFilter } from "./channelColumns";
@@ -110,6 +109,7 @@ export default function Channels() {
   const [tagManagerOpen, setTagManagerOpen] = useState(false);
   const unblock = useMutation({
     mutationFn: (id: string) => api.unblockChannel(id),
+    meta: { failTitle: "errors.writeFailed.unblockChannel" },
     onSuccess: () => {
       qc.invalidateQueries({ queryKey: qk.blockedChannels() });
       qc.invalidateQueries({ queryKey: qk.feed() });
@@ -133,6 +133,7 @@ export default function Channels() {
       id: string;
       body: { priority?: number; hidden?: boolean; deep_requested?: boolean };
     }) => api.updateChannel(v.id, v.body),
+    meta: { failTitle: "errors.writeFailed.channelSettings" },
     // Requesting full history may have just pulled in a channel's recent uploads, so
     // refresh the per-user status and feed too — not only the channel list.
     onSuccess: () => {
@@ -182,11 +183,10 @@ export default function Channels() {
     // A failed attach/detach reverts the optimistic change by refetching the list. Also refetch
     // suggestions: acceptSuggestion optimistically dropped the channel from that cache, and on
     // failure the tag never actually attached — so the server still suggests it and the ghost chips
-    // must come back rather than leaving an empty cell (honest states). Surface the write failure too.
-    onError: (e) => {
+    // must come back rather than leaving an empty cell (honest states). The hook reports the failure.
+    onError: () => {
       qc.invalidateQueries({ queryKey: qk.channels() });
       qc.invalidateQueries({ queryKey: qk.tagSuggestions() });
-      notifyActionError(e, t("channels.tags.updateFailed"));
     },
   });
   // --- Suggested tags (E8·S4): learned from the user's own manual-tag pattern, shown as accept/dismiss

frontend/src/components/DownloadCenter.tsx

@@ -34,6 +34,7 @@ import { useConfirm } from "./ConfirmProvider";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { useMe } from "../lib/useMe";
 import { api, type DownloadJob } from "../lib/api";
+import { notifyActionError } from "../lib/actionErrors";
 import { invalidateDownloads, quickShareLink } from "../lib/downloads";
 import { libraryRowActions, sharedRowActions } from "../lib/downloadActions";
 import { inputCls } from "./ui/form";
@@ -95,14 +96,16 @@ export default function DownloadCenter() {
               ? api.redownloadDownload(id)
               : api.deleteDownload(id),
     onSuccess: invalidate,
-    // No onError: a failed job action returns 400/409/422/500, already surfaced by the global
-    // error modal (api.ts req) with the backend's specific message — a caller toast would double it.
+    // A 400/409/422/500 opens the global error dialog with the backend's own message (and is then
+    // skipped here); a job that is gone (404) or a lost connection is said here, naming the action.
+    onError: (e, v) => notifyActionError(e, t(`errors.writeFailed.job.${v.op}`)),
   });
 
   // Remove a shared-with-me item from your list (only your grant; the owner's file is untouched).
   const removeShared = useMutation({
     mutationFn: (id: number) => api.removeSharedDownload(id),
     onSuccess: () => qc.invalidateQueries({ queryKey: qk.downloadsShared() }),
+    meta: { failTitle: "errors.writeFailed.removeShared" },
   });
 
   const confirmThen = async (title: string, body: string, fn: () => void) => {

frontend/src/components/DownloadDialog.tsx

@@ -10,6 +10,7 @@ import { invalidateDownloads } from "../lib/downloads";
 // Lazy: the full profile editor only opens from the dialog's "manage presets" affordance.
 const ProfileEditor = lazy(() => import("./ProfileEditor"));
 import { notify } from "../lib/notifications";
+import { notifyActionError } from "../lib/actionErrors";
 import { navigateTo } from "../lib/nav";
 import { inputCls } from "./ui/form";
 
@@ -51,8 +52,11 @@ export default function DownloadDialog({
         action: { label: t("downloads.dialog.view"), onClick: () => navigateTo("downloads") },
       });
       onClose();
-    } catch {
-      // Non-quiet request: the global error dialog already surfaced the reason (e.g. quota).
+    } catch (e) {
+      // A quota or validation refusal (422/409) is already in the global error dialog, which the
+      // reporter skips; a 403/404/429 or a lost connection is not, and used to leave the dialog
+      // open with nothing said (E11 S2b).
+      notifyActionError(e, t("errors.writeFailed.enqueueDownload"));
       setBusy(false);
     }
   };

frontend/src/components/Feed.tsx

@@ -23,6 +23,7 @@ import {
 } from "lucide-react";
 import { api, HttpError, type FeedFilters, type Video, type VideoStatus } from "../lib/api";
 import i18n from "../i18n";
+import { notifyActionError } from "../lib/actionErrors";
 import { notify, resolveVideo } from "../lib/notifications";
 import { useDebounced } from "../lib/useDebounced";
 import {
@@ -308,15 +309,17 @@ export default function Feed({
             resolveVideo(id);
           }
         })
-        .catch(() =>
+        .catch((e: unknown) => {
           // Server rejected the change — drop the optimistic override so the card
-          // reverts to the real (unchanged) state instead of staying phantom-hidden.
+          // reverts to the real (unchanged) state instead of staying phantom-hidden, and say so:
+          // a card that silently snaps back reads as a misclick.
+          notifyActionError(e, i18n.t("errors.writeFailed.videoState"));
           setOverrides((o) => {
             const next = { ...o };
             delete next[id];
             return next;
-          }),
-        );
+          });
+        });
     },
     [qc],
   );
@@ -330,13 +333,14 @@ export default function Feed({
         .clearState(id)
         // Stale-mark only (see setState above): the optimistic override already reset the card.
         .then(() => qc.invalidateQueries({ queryKey: qk.feed(), refetchType: "none" }))
-        .catch(() =>
+        .catch((e: unknown) => {
+          notifyActionError(e, i18n.t("errors.writeFailed.videoReset"));
           setOverrides((o) => {
             const next = { ...o };
             delete next[id];
             return next;
-          }),
-        );
+          });
+        });
     },
     [qc],
   );
@@ -349,7 +353,15 @@ export default function Feed({
           qc.invalidateQueries({ queryKey: qk.playlists() });
           qc.invalidateQueries({ queryKey: qk.playlist() });
         })
-        .catch(() => setSavedOverrides((o) => ({ ...o, [id]: !saved })));
+        .catch((e: unknown) => {
+          notifyActionError(
+            e,
+            i18n.t(
+              saved ? "errors.writeFailed.watchLaterAdd" : "errors.writeFailed.watchLaterRemove",
+            ),
+          );
+          setSavedOverrides((o) => ({ ...o, [id]: !saved }));
+        });
     },
     [qc],
   );
@@ -466,7 +478,9 @@ export default function Feed({
                     .then((r) =>
                       notify({ message: i18n.t("feed.yt.cleared", { count: r.removed }) }),
                     )
-                    .catch(() => {});
+                    .catch((e: unknown) =>
+                      notifyActionError(e, i18n.t("errors.writeFailed.clearSearch")),
+                    );
                   setFilters({ ...filters, librarySource: "organic", sort: "newest" });
                   onExitYtSearch();
                   dropFeedCaches();

frontend/src/components/NotificationsPanel.tsx

@@ -79,10 +79,26 @@ export default function NotificationsPanel() {
     qc.invalidateQueries({ queryKey: qk.notifications() });
     qc.invalidateQueries({ queryKey: qk.notifUnread() });
   };
-  const readMut = useMutation({ mutationFn: api.markNotificationRead, onSuccess: refresh });
-  const readAllMut = useMutation({ mutationFn: api.markAllNotificationsRead, onSuccess: refresh });
-  const dismissMut = useMutation({ mutationFn: api.dismissNotification, onSuccess: refresh });
-  const clearMut = useMutation({ mutationFn: api.clearNotifications, onSuccess: refresh });
+  const readMut = useMutation({
+    mutationFn: api.markNotificationRead,
+    onSuccess: refresh,
+    meta: { failTitle: "errors.writeFailed.notifRead" },
+  });
+  const readAllMut = useMutation({
+    mutationFn: api.markAllNotificationsRead,
+    onSuccess: refresh,
+    meta: { failTitle: "errors.writeFailed.notifReadAll" },
+  });
+  const dismissMut = useMutation({
+    mutationFn: api.dismissNotification,
+    onSuccess: refresh,
+    meta: { failTitle: "errors.writeFailed.notifDismiss" },
+  });
+  const clearMut = useMutation({
+    mutationFn: api.clearNotifications,
+    onSuccess: refresh,
+    meta: { failTitle: "errors.writeFailed.notifClear" },
+  });
 
   const serverUnread = serverItems.some((n) => !n.read);
   const hasAny = serverItems.length > 0 || clientItems.length > 0;

frontend/src/components/OnboardingWizard.tsx

@@ -82,6 +82,8 @@ export default function OnboardingWizard({ me, onClose }: { me: Me; onClose: ()
       qc.invalidateQueries({ queryKey: qk.channels() });
       qc.invalidateQueries({ queryKey: qk.myStatus() });
     },
+    // The step itself says the import failed and offers a retry button — no toast on top.
+    meta: { errorShownInline: true },
   });
 
   // First time we see read access with zero imported channels, pull the user's

frontend/src/components/Playlists.dom.test.tsx

@@ -380,7 +380,7 @@ describe("Playlists — a change the server refused is taken back on screen", ()
     await act(async () => void (await new Promise((r) => setTimeout(r, 20))));
     expect(rowsOnScreen()).toEqual(["Video V", "Video W"]);
     expect(h.notify).toHaveBeenCalledWith(
-      expect.objectContaining({ level: "error", message: "playlists.removeFailed" }),
+      expect.objectContaining({ level: "error", title: "playlists.removeFailed" }),
     );
   });
 });

frontend/src/components/Playlists.tsx

@@ -676,13 +676,17 @@ export default function Playlists() {
   }
 
   function playerState(id: string, status: string) {
-    api.setState(id, status).then(() => {
-      // Every cached list, not `qk.playlist(selectedId)`: the player may have been launched from a
-      // list that is no longer the selected one (see `playing`), and that list holds the row whose
-      // status just changed. Only lists actually on screen refetch.
-      qc.invalidateQueries({ queryKey: qk.playlist() });
-      qc.invalidateQueries({ queryKey: qk.feed() });
-    });
+    api
+      .setState(id, status)
+      .then(() => {
+        // Every cached list, not `qk.playlist(selectedId)`: the player may have been launched from a
+        // list that is no longer the selected one (see `playing`), and that list holds the row whose
+        // status just changed. Only lists actually on screen refetch.
+        qc.invalidateQueries({ queryKey: qk.playlist() });
+        qc.invalidateQueries({ queryKey: qk.feed() });
+      })
+      // No catch used to mean an unhandled rejection and nothing said (E11 S2b).
+      .catch((e: unknown) => notifyActionError(e, t("errors.writeFailed.videoState")));
   }
 
   // Stable identity: PlayerModal's keydown/scroll-lock effect depends on it, so a fresh closure

frontend/src/components/PlaylistsRail.tsx

@@ -160,6 +160,7 @@ export default function PlaylistsRail({
 
   const createMut = useMutation({
     mutationFn: (name: string) => api.createPlaylist(name),
+    meta: { failTitle: "errors.writeFailed.createPlaylist" },
     onSuccess: (pl: Playlist) => {
       setNewName("");
       qc.invalidateQueries({ queryKey: qk.playlists() });

frontend/src/components/PlexSidebar.tsx

@@ -6,6 +6,7 @@ import { plexLang } from "../i18n";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { ListMusic, Plus, SlidersHorizontal, X } from "lucide-react";
 import { api, plexFilterCount, type PlexFilters } from "../lib/api";
+import { notifyActionError } from "../lib/actionErrors";
 import { type PanelLayout } from "../lib/panelLayout";
 import { type MediaSourceKind } from "../lib/mediaSource";
 import { useDebounced } from "../lib/useDebounced";
@@ -377,9 +378,14 @@ function PlaylistPicker() {
   ];
 
   async function createPlaylist(title: string) {
-    const pl = await api.plexCreatePlaylist(title);
-    qc.invalidateQueries({ queryKey: qk.plexPlaylists() });
-    onOpenPlaylist(pl.id);
+    try {
+      const pl = await api.plexCreatePlaylist(title);
+      qc.invalidateQueries({ queryKey: qk.plexPlaylists() });
+      onOpenPlaylist(pl.id);
+    } catch (e) {
+      // Called without an await from the picker, so a refusal was an unhandled rejection (E11 S2b).
+      notifyActionError(e, t("plex.playlistAdd.createFailed"));
+    }
   }
 
   return (

frontend/src/components/ProfileEditor.tsx

@@ -77,10 +77,12 @@ export default function ProfileEditor({ onClose }: { onClose: () => void }) {
       invalidate();
       setFormOpen(false);
     },
+    meta: { failTitle: "errors.writeFailed.downloadProfileSave" },
   });
   const del = useMutation({
     mutationFn: (id: number) => api.deleteDownloadProfile(id),
     onSuccess: invalidate,
+    meta: { failTitle: "errors.writeFailed.downloadProfileDelete" },
   });
 
   const onDelete = async (p: DownloadProfile) => {

frontend/src/components/Scheduler.tsx

@@ -390,6 +390,7 @@ export default function Scheduler() {
   // live poll surfaces the "running" state within a tick, so we just nudge a refetch.
   const runMut = useMutation({
     mutationFn: (jobId: string) => api.runSchedulerJob(jobId),
+    meta: { failTitle: "errors.writeFailed.schedulerRun" },
     onSuccess: (_d, jobId) => {
       notify({
         level: "success",
@@ -400,6 +401,7 @@ export default function Scheduler() {
   });
   const runAllMut = useMutation({
     mutationFn: () => api.runAllSchedulerJobs(),
+    meta: { failTitle: "errors.writeFailed.schedulerRunAll" },
     onSuccess: (res) => {
       notify({
         level: "success",
@@ -410,10 +412,12 @@ export default function Scheduler() {
   });
   const batchMut = useMutation({
     mutationFn: (v: number) => api.updateMaintenanceBatch(v),
+    meta: { failTitle: "errors.writeFailed.maintenanceBatch" },
     onSuccess: () => qc.invalidateQueries({ queryKey: qk.scheduler() }),
   });
   const purgeMut = useMutation({
     mutationFn: () => api.purgeDiscovery(),
+    meta: { failTitle: "errors.writeFailed.purgeDiscovery" },
     onSuccess: (res) => {
       const removed =
         (res.search_videos_deleted ?? 0) + (res.videos_deleted ?? 0) + (res.channels_deleted ?? 0);

frontend/src/components/SettingsPanel.tsx

@@ -6,6 +6,7 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { Bell, Check, Loader2, Monitor, RefreshCw, Trash2, User } from "lucide-react";
 import { SCHEMES, type Scheme, type ThemePrefs } from "../lib/theme";
 import { api, HttpError, type Me } from "../lib/api";
+import { notifyActionError } from "../lib/actionErrors";
 import { LS, useAccountPersistedState } from "../lib/storage";
 import Avatar from "./ui/Avatar";
 import { notify, type NotifSettings } from "../lib/notifications";
@@ -553,10 +554,11 @@ function PlexWatchSync() {
   };
 
   // No onError on these: they're Plex, not YouTube (notifyYouTubeActionError would wrongly say
-  // "connect YouTube"), and their 409/500 are already surfaced by the global error modal — a caller
-  // toast would double it. Actual import failures come back as 200 {error}, handled by announce.
+  // "connect YouTube"). Their 409/500 open the global error dialog and the rest go to the app-wide
+  // reporter (lib/queryClient). Actual import failures come back as 200 {error}, handled by announce.
   const toggle = useMutation({
     mutationFn: (next: boolean) => api.plexWatchSetLink(next),
+    meta: { failTitle: "errors.writeFailed.plexWatchLink" },
     onSuccess: (res) => {
       qc.setQueryData(qk.plexWatchLink(), res);
       announce(res.import);
@@ -564,6 +566,7 @@ function PlexWatchSync() {
   });
   const reimport = useMutation({
     mutationFn: () => api.plexWatchImport(),
+    meta: { failTitle: "errors.writeFailed.plexWatchImport" },
     onSuccess: (res) => {
       qc.setQueryData(qk.plexWatchLink(), res);
       announce(res.import);
@@ -637,10 +640,13 @@ export function DownloadAuth() {
       notify({ level: "success", message: t("settings.downloadAuth.saved") });
     },
     // Validation errors (empty / not-a-cookies.txt) surface via the global error modal, which
-    // localizes the structured { code: "cookies" } detail (see lib/api core localizeDetail).
+    // localizes the structured { code: "cookies" } detail (see lib/api core localizeDetail); the
+    // statuses it does not cover go to the app-wide reporter.
+    meta: { failTitle: "settings.downloadAuth.failed" },
   });
   const remove = useMutation({
     mutationFn: (host: string) => api.deleteDownloadCredential(host),
+    meta: { failTitle: "errors.writeFailed.downloadCookiesRemove" },
     onSuccess: (res) => {
       qc.setQueryData(qk.downloadCredentials(), res);
       notify({ level: "success", message: t("settings.downloadAuth.removed") });
@@ -781,8 +787,10 @@ function Account({ me, onOpenWizard }: { me: Me; onOpenWizard: () => void }) {
       await api.deleteAccount();
       // Session cleared server-side → /api/me 401s → Welcome. The flag shows the confirmation banner.
       window.location.href = "/?deleted=1";
-    } catch {
-      /* the global error dialog surfaces the reason (e.g. last admin) */
+    } catch (e) {
+      // A refusal with a reason (the last admin, a 409) is already in the global error dialog, which
+      // the reporter skips; anything else used to end the confirmed delete with nothing said.
+      notifyActionError(e, t("errors.writeFailed.deleteAccount"));
     }
   };
   return (

frontend/src/components/ShareDialog.tsx

@@ -106,15 +106,18 @@ function LinkRow({ link, onChanged }: { link: ShareLink; onChanged: () => void }
   const toggle = useMutation({
     mutationFn: () => api.updateDownloadLink(link.id, { allow_download: !link.allow_download }),
     onSuccess: onChanged,
+    meta: { failTitle: "errors.writeFailed.shareLinkDownload" },
   });
   const revoke = useMutation({
     mutationFn: () => api.revokeDownloadLink(link.id),
     onSuccess: onChanged,
+    meta: { failTitle: "errors.writeFailed.shareLinkRevoke" },
   });
   // Set / change / clear the link password. Rotating (or clearing) it bumps the link's
   // password_version server-side, which invalidates any watch grant issued under the old password.
   const savePass = useMutation({
     mutationFn: (pw: string) => api.updateDownloadLink(link.id, { password: pw }),
+    meta: { failTitle: "errors.writeFailed.shareLinkPassword" },
     onSuccess: () => {
       setEditPass(false);
       setNewPass("");
@@ -282,6 +285,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
       setExpiryDays(null);
       setPassword("");
     },
+    meta: { failTitle: "downloads.share.linkFailed" },
   });
 
   // Open with a link already generated: sharing is almost always the goal, so mint a default

frontend/src/components/Stats.tsx

@@ -210,6 +210,11 @@ function SystemStats() {
   const pauseResume = useMutation({
     mutationFn: (paused: boolean) => (paused ? api.resumeSync() : api.pauseSync()),
     onSuccess: () => qc.invalidateQueries({ queryKey: qk.myStatus() }),
+    onError: (e, paused) =>
+      notifyActionError(
+        e,
+        t(paused ? "errors.writeFailed.syncResume" : "errors.writeFailed.syncPause"),
+      ),
   });
   const data = q.data;
   const maxDaily = Math.max(1, ...(data?.daily ?? []).map((d) => d.total));

frontend/src/components/SyncStatus.tsx

@@ -4,6 +4,7 @@ import { qk } from "../lib/queryKeys";
 import { useTranslation } from "react-i18next";
 import { CheckCircle2, Clock, Database, History, Loader2, Pause, Play } from "lucide-react";
 import { api, type MyStatus } from "../lib/api";
+import { notifyActionError } from "../lib/actionErrors";
 import { formatViews } from "../lib/format";
 import { PopoverSurface, useAnchoredPopover } from "./ui/AnchoredPopover";
 
@@ -53,6 +54,11 @@ export default function SyncStatus({
   const toggle = useMutation({
     mutationFn: () => (data?.paused ? api.resumeSync() : api.pauseSync()),
     onSuccess: () => qc.invalidateQueries({ queryKey: qk.myStatus() }),
+    onError: (e) =>
+      notifyActionError(
+        e,
+        t(data?.paused ? "errors.writeFailed.syncResume" : "errors.writeFailed.syncPause"),
+      ),
   });
 
   if (!data) return null;

frontend/src/components/TagManager.tsx

@@ -129,6 +129,7 @@ export default function TagManager({
   };
   const create = useMutation({
     mutationFn: (name: string) => api.createTag({ name, category: "other" }),
+    meta: { failTitle: "channels.tags.createFailed" },
     onSuccess: () => {
       setNewName("");
       invalidate();

frontend/src/components/WriteFailureReporting.dom.test.tsx

@@ -19,7 +19,7 @@ vi.mock("react-i18next", async (importOriginal) => {
 });
 vi.mock("./ConfirmProvider", () => ({ useConfirm: () => async () => true }));
 const { notify } = vi.hoisted(() => ({
-  notify: vi.fn((_n: { level: string; message: string }) => 0),
+  notify: vi.fn((_n: { level: string; title?: string; message: string }) => 0),
 }));
 vi.mock("../lib/notifications", async (importOriginal) => ({
   ...(await importOriginal<typeof import("../lib/notifications")>()),
@@ -28,6 +28,7 @@ vi.mock("../lib/notifications", async (importOriginal) => ({
 
 import PlexCollectionEditor from "./PlexCollectionEditor";
 import UploadDialog from "./UploadDialog";
+import DownloadDialog from "./DownloadDialog";
 import { api, HttpError } from "../lib/api";
 
 beforeAll(() => {
@@ -48,7 +49,9 @@ afterEach(() => {
   vi.restoreAllMocks();
 });
 
-const errors = () => notify.mock.calls.filter(([n]) => n.level === "error").map(([n]) => n.message);
+// What failed, as the toast names it: the title (E11 S2b — the title says WHAT, the line under it WHY).
+const errors = () =>
+  notify.mock.calls.filter(([n]) => n.level === "error").map(([n]) => n.title ?? n.message);
 const client = () => new QueryClient({ defaultOptions: { queries: { retry: false } } });
 
 describe("the Plex collection editor", () => {
@@ -144,3 +147,20 @@ describe("the upload dialog", () => {
     expect(errors()).toEqual([]);
   });
 });
+
+describe("the download dialog", () => {
+  it("names a queueing the server refused with no dialog of its own", async () => {
+    // Its catch said "the global error dialog already surfaced the reason" — true for a quota 422,
+    // not for a 403/404/429 or a lost connection, where the dialog just stayed open (E11 S2b).
+    vi.spyOn(api, "downloadProfiles").mockResolvedValue([{ id: 1, name: "Best" }] as never);
+    vi.spyOn(api, "enqueueDownload").mockRejectedValue(new HttpError(403, "nope"));
+    render(
+      <QueryClientProvider client={client()}>
+        <DownloadDialog source="https://example.com/v" onClose={() => {}} />
+      </QueryClientProvider>,
+    );
+    await screen.findByText("Best");
+    fireEvent.click(screen.getByText("downloads.dialog.submit"));
+    await waitFor(() => expect(errors()).toEqual(["errors.writeFailed.enqueueDownload"]));
+  });
+});

frontend/src/components/accountPanel.dom.test.tsx

@@ -87,11 +87,13 @@ beforeEach(() => {
 });
 afterEach(cleanup);
 
+// What each error toast names: its title when it has one (a failure reported with its reason under
+// it — E11 S2b), else the specific sentence (the no-mail case).
 const errorMessages = () =>
   notifyMock.mock.calls
-    .map(([a]) => a as { level?: string; message?: string })
+    .map(([a]) => a as { level?: string; title?: string; message?: string })
     .filter((a) => a.level === "error")
-    .map((a) => a.message);
+    .map((a) => a.title ?? a.message);
 
 describe("the account panel reports a refused recovery action", () => {
   it("says the link could not be minted instead of leaving the button inert", async () => {

frontend/src/components/downloadAdmin.tsx

@@ -62,10 +62,12 @@ function QuotaModal({
         unlimited: state!.unlimited,
       }),
     onSuccess: done,
+    meta: { failTitle: "errors.writeFailed.downloadQuota" },
   });
   const reset = useMutation({
     mutationFn: () => api.adminResetDownloadQuota(userId),
     onSuccess: done,
+    meta: { failTitle: "errors.writeFailed.downloadQuotaReset" },
   });
   if (!state) return null;
   const upd = (p: Partial<typeof state>) => setForm({ ...state, ...p });

frontend/src/components/downloadModals.tsx

@@ -41,6 +41,7 @@ export function MetaEditModal({ job, onClose }: { job: DownloadJob; onClose: ()
       qc.invalidateQueries({ queryKey: qk.downloads() });
       onClose();
     },
+    meta: { failTitle: "errors.writeFailed.downloadDetails" },
   });
 
   return (

frontend/src/components/usePlaylistActions.dom.test.tsx

@@ -61,13 +61,16 @@ describe("usePlaylistActions — deleting a list", () => {
   });
 
   it("does say one it was left to handle — in the reader's language", async () => {
-    // A plain-string `detail` is whatever English the route hand-wrote; the caller's own translated
-    // fallback is the one a Hungarian reader can read (deep-review round 5).
+    // A plain-string `detail` is whatever English the route hand-wrote, so it is never shown: the
+    // caller's translated title says what failed, and the status says why (deep-review round 5, S2b).
     vi.spyOn(api, "deletePlaylist").mockRejectedValue(new HttpError(404, "Unknown playlist"));
     const { result } = mount();
     await act(() => result.current.remove(linked));
     expect(h.notify).toHaveBeenCalledWith(
-      expect.objectContaining({ message: "playlists.deleteYtFailed" }),
+      expect.objectContaining({ title: "playlists.deleteYtFailed" }),
+    );
+    expect(h.notify).not.toHaveBeenCalledWith(
+      expect.objectContaining({ message: "Unknown playlist" }),
     );
   });