feat(channels): the band's tag chips and status row fold on a short window (B4)

Every other page band folds its filter row below ~600px of height; the Channels band never did, so
its tag chip lane and status / pager row kept a short laptop window for themselves. They fold behind
one "Filters · n" (n = picked tags + other active column filters); the tabs and the TAGS editor stay,
and a folded table keeps its controls at the list's end.

frontend/src/components/Channels.tsx

@@ -37,7 +37,9 @@ import ChannelStatsPopover from "./ChannelStatsPopover";
 import Pager from "./ui/Pager";
 import { CHANNEL_LAYOUTS, type ChannelLayout } from "../lib/channelLayout";
 import { sortRows } from "../lib/columnSort";
-import { filterRows } from "../lib/tableColumns";
+import { filterRows, isActive } from "../lib/tableColumns";
+import { useFilterFold } from "../lib/useFilterFold";
+import { FilterFoldButton } from "./ui/FilterFold";
 import { useCardPager } from "../lib/useCardPager";
 import { PageToolbar } from "./ui/PageShell";
 import { PageMenu } from "./ui/PageMenu";
@@ -243,6 +245,13 @@ export default function Channels() {
   // funnel share ONE state and stay in sync (bidirectional). Toggling a chip rewrites `filters.tags`;
   // filterRows / DataTable then applies it. Channel-name search stays separate (the shared top box).
   const tagFilter = Array.isArray(filters.tags) ? filters.tags : [];
+  // B4 (E28 review L7): on a short window the band's filters — the tag chip lane and the status /
+  // pager row — fold behind one "Filters · n"; the tabs and the TAGS editor stay. n = each picked tag,
+  // plus every other active column filter (the status chips are the Sync column's).
+  const fold = useFilterFold();
+  const foldCount =
+    tagFilter.length +
+    Object.entries(filters).filter(([k, v]) => k !== "tags" && isActive(v)).length;
   // Picking a real tag drops the "No tag" sentinel (item B) — they're mutually exclusive, as in the feed.
   const toggleTagFilter = (tagId: number) => {
     const id = String(tagId);
@@ -609,8 +618,9 @@ export default function Channels() {
                   {t("channels.tags.label")}
                 </Button>
               </Tooltip>
-              <TagFilterChips chips={tagFilterChips} className="flex-1" />
-              {tagFilter.length > 0 && (
+              <FilterFoldButton fold={fold} label={t("sidebar.filters")} count={foldCount} />
+              {!fold.folded && <TagFilterChips chips={tagFilterChips} className="flex-1" />}
+              {!fold.folded && tagFilter.length > 0 && (
                 <Button
                   variant="link-muted"
                   onClick={() => setFilters({ ...filters, tags: [] })}
@@ -646,7 +656,7 @@ export default function Channels() {
         )}
         {/* In table mode the status chips + pager ride in DataTable's own in-band controls row. The card
         layout has no such row, so surface the same status chips (left) and its pager (right) here. */}
-        {view === "subscribed" && layout === "cards" && (
+        {view === "subscribed" && layout === "cards" && !fold.folded && (
           <div className="px-4 pb-2 max-w-384 mx-auto flex items-center justify-between gap-3 flex-wrap">
             {statusChips}
             {cardPager}
@@ -717,7 +727,8 @@ export default function Channels() {
                 columns={columns}
                 rowKey={(c) => c.id}
                 persistKey={accountKey(LS.channelsTable) ?? undefined}
-                controlsPosition="both"
+                // Folded, the status / pager row leaves the band; the list's own end keeps it.
+                controlsPosition={fold.folded ? "bottom" : "both"}
                 controlsLeading={statusChips}
                 controlsInBand
                 controlsBandClassName="px-4 max-w-384 mx-auto"

frontend/src/components/channelsTagRow.contract.test.ts

@@ -22,3 +22,16 @@ describe("the Channels tag row", () => {
     expect(block).toContain("@max-[40rem]/tagrow:basis-full");
   });
 });
+
+// E28 review L7: every other page band folds its filter row on a short window (B4, `useFilterFold`);
+// the Channels band never did — its tag chips and the status / pager row kept a laptop's short window
+// for themselves. They fold behind one "Filters · n", the tabs and the TAGS editor stay.
+describe("the Channels band on a short window", () => {
+  it("folds the tag chip lane and the status / pager row behind the fold button", () => {
+    expect(src).toContain("const fold = useFilterFold();");
+    expect(src).toMatch(/<FilterFoldButton\s[^>]*fold=\{fold\}/);
+    expect(src).toMatch(/!fold\.folded && <TagFilterChips/);
+    expect(src).toMatch(/controlsPosition=\{fold\.folded \? "bottom" : "both"\}/);
+    expect(src).toMatch(/layout === "cards" && !fold\.folded/);
+  });
+});