fix(e8): deep-review hardening + cut 0.73.0

Fixes from several multi-agent deep-review passes over the E8 feed-filtering &
channel-manager epic (S1-S4):
- feed_years buckets by UTC year to match the UTC-pinned year-filter bounds
- tag suggestions: examples ∩ subscribed (drop tagged-then-unsubscribed channels
  from the profile denominator); exclude hidden channels as suggestion targets
- channel manager: restore ghost chips + surface an error toast on a failed tag accept
- year filter: debounce the search term so the per-year facet doesn't refetch per keystroke
- channel tags: aria-label the "+N" overflow pills
- extract useTagSuggestions hook; add backend + hook tests (profile boundaries, cap,
  language exclusion, unsubscribed/hidden handling, UTC bucketing, bulk-accept)

Bump VERSION to 0.73.0 + release notes.

frontend/src/components/Channels.tsx

@@ -4,9 +4,8 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
 import { Ban, Eye, EyeOff, History, LayoutGrid, Pencil, RefreshCw, Table, X } from "lucide-react";
 import ExcludedChannelList from "./ExcludedChannelList";
-import { api, NO_TAG_SENTINEL, type ManagedChannel, type TagSuggestions } from "../lib/api";
+import { api, NO_TAG_SENTINEL, type ManagedChannel } from "../lib/api";
 import { Sparkles } from "lucide-react";
-import type { SuggestedTag } from "./ChannelTags";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
 import { accountKey, LS } from "../lib/storage";
 import { buildChannelColumns, applySyncFilter } from "./channelColumns";
@@ -17,6 +16,7 @@ import Tabs, { type TabDef } from "./Tabs";
 import ChannelLayoutGrid from "./ChannelLayoutGrid";
 import { LoadingState, StateMessage } from "./QueryState";
 import { useChannelTagActions } from "../lib/useChannelTagActions";
+import { useTagSuggestions } from "./useTagSuggestions";
 import { useChannelPriority } from "../lib/useChannelPriority";
 import ViewSwitcher, { type ViewOption } from "./ViewSwitcher";
 import ColumnSortControl from "./ColumnSortControl";
@@ -56,11 +56,6 @@ const LAYOUT_ICON: Record<ChannelLayout, typeof Table> = {
   cards: LayoutGrid,
 };
 
-// A tag suggestion at/above this score is "high confidence" — the only ones the header's bulk
-// "accept all" acts on. Mirrors AUTOAPPLY_THRESHOLD in backend app/sync/tagsuggest.py (kept in
-// lockstep by intent: the two aren't imported across the stack, so a change must touch both).
-const HIGH_CONFIDENCE = 0.9;
-
 export default function Channels() {
   const me = useMe();
   const canWrite = me.can_write;
@@ -105,10 +100,6 @@ export default function Channels() {
 
   const channelsQuery = useQuery({ queryKey: qk.channels(), queryFn: api.channels });
   const tagsQuery = useQuery({ queryKey: qk.tags(), queryFn: api.tags });
-  const suggestionsQuery = useQuery({
-    queryKey: qk.tagSuggestions(),
-    queryFn: api.tagSuggestions,
-  });
   const statusQuery = useQuery({ queryKey: qk.myStatus(), queryFn: api.myStatus });
   const blockedQuery = useQuery({ queryKey: qk.blockedChannels(), queryFn: api.blockedChannels });
   const [tagManagerOpen, setTagManagerOpen] = useState(false);
@@ -183,56 +174,29 @@ export default function Channels() {
       qc.invalidateQueries({ queryKey: qk.channel(id) });
       qc.invalidateQueries({ queryKey: qk.tagSuggestions() });
     },
-    onError: () => qc.invalidateQueries({ queryKey: qk.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: () => {
+      qc.invalidateQueries({ queryKey: qk.channels() });
+      qc.invalidateQueries({ queryKey: qk.tagSuggestions() });
+      notify({ level: "error", message: t("channels.tags.updateFailed") });
+    },
   });
   // --- Suggested tags (E8·S4): learned from the user's own manual-tag pattern, shown as accept/dismiss
   // ghost chips on untagged channels. Dismissal is session-only (an accepted suggestion self-clears —
-  // the channel becomes tagged and the server drops it; a dismissed one just hides until reload).
-  const tagById = useMemo(
-    () => new Map((tagsQuery.data ?? []).map((tg) => [tg.id, tg])),
-    [tagsQuery.data],
-  );
-  const [dismissed, setDismissed] = useState<Set<string>>(() => new Set());
-  const suggestions: TagSuggestions = suggestionsQuery.data ?? {};
-  const sKey = (cid: string, tagId: number) => `${cid}:${tagId}`;
-  // Resolve a channel's raw {tag_id, confidence} list to renderable {tag, confidence}, dropping any
-  // that were dismissed this session or whose tag no longer exists (deleted since the last compute).
-  const suggestionsFor = (cid: string): SuggestedTag[] =>
-    (suggestions[cid] ?? []).flatMap((s) => {
-      const tag = tagById.get(s.tag_id);
-      return tag && !dismissed.has(sKey(cid, s.tag_id)) ? [{ tag, confidence: s.confidence }] : [];
-    });
-  const dismissSuggestion = (cid: string, tagId: number) =>
-    setDismissed((prev) => new Set(prev).add(sKey(cid, tagId)));
-  const acceptSuggestion = (cid: string, tagId: number) => {
-    // Optimistically drop the WHOLE channel from the suggestions cache: attaching any tag makes it
-    // "tagged", which the server excludes from suggestions entirely — so its other ghost chips would
-    // vanish on the next refetch anyway. Removing them now keeps the ghost lane and the attached lane
-    // mutually exclusive (no transient of both showing). toggleTag attaches the real tag; its onSuccess
-    // re-invalidates suggestions + the channel detail.
-    qc.setQueryData<TagSuggestions>(qk.tagSuggestions(), (old) => {
-      if (!old?.[cid]) return old;
-      const next = { ...old };
-      delete next[cid];
-      return next;
-    });
-    toggleTag(cid, tagId, false);
-  };
-  // Every currently-visible suggestion (all channels, minus dismissed) and the high-confidence subset
-  // the bulk action accepts.
-  const visibleSuggestions = Object.keys(suggestions).flatMap((cid) =>
-    suggestionsFor(cid).map((s) => ({ cid, tagId: s.tag.id, confidence: s.confidence })),
-  );
-  const highConfidence = visibleSuggestions.filter((s) => s.confidence >= HIGH_CONFIDENCE);
-  const acceptAllHighConfidence = async () => {
-    const ok = await confirm({
-      title: t("channels.tags.acceptAllTitle"),
-      message: t("channels.tags.acceptAllConfirm", { count: highConfidence.length }),
-      confirmLabel: t("channels.tags.acceptAllConfirmCta"),
-    });
-    if (!ok) return;
-    highConfidence.forEach(({ cid, tagId }) => acceptSuggestion(cid, tagId));
-  };
+  // the channel becomes tagged and the server drops it; a dismissed one just hides until reload). The
+  // /tags/suggestions query, the session dismiss set, and the optimistic accept/dismiss/bulk logic all
+  // live in useTagSuggestions so they can be unit-tested apart from this component.
+  const {
+    suggestionsFor,
+    dismissSuggestion,
+    acceptSuggestion,
+    visibleSuggestions,
+    highConfidence,
+    acceptAllHighConfidence,
+  } = useTagSuggestions({ tags: tagsQuery.data ?? [], toggleTag });
 
   const syncSubs = useMutation({
     mutationFn: () => api.syncSubscriptions(),