feat(channels): surface full-history pull + honest stored/total count on the channel page (S3)

The catalog only stores the recent-backfill/RSS subset of a channel's uploads (video_count is
YouTube's raw total), so a subscribed channel looked like it was "missing" videos. Now the channel
page header shows "{stored} / {total} videos" when there's a gap, and a "Full history" action queues
the deep backfill (the same deep_requested trigger the channel manager uses) — showing a loading
state until done. Backend: channel_detail now returns deep_requested/backfill_done.

frontend/src/components/ChannelPage.tsx

@@ -8,6 +8,7 @@ import {
   Ban,
   Check,
   ExternalLink,
+  History,
   Loader2,
   Plus,
   RefreshCw,
@@ -150,6 +151,21 @@ export default function ChannelPage({
     },
     onError: (err) => notifyYouTubeActionError(err, t("channels.notify.unsubscribeFailed")),
   });
+  // "Get full history": the catalog only holds the recent-backfill/RSS subset of a channel's
+  // uploads (video_count is YouTube's raw total), so flipping deep_requested queues the full
+  // back-catalog pager. Same trigger the channel manager uses.
+  const deepBackfill = useMutation({
+    mutationFn: () => api.updateChannel(channelId, { deep_requested: true }),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: qk.channel(channelId) });
+      qc.invalidateQueries({ queryKey: qk.feed() });
+      qc.invalidateQueries({ queryKey: qk.channels() });
+      qc.invalidateQueries({ queryKey: qk.myStatus() });
+      notify({ level: "info", message: t("channel.fullHistoryQueued") });
+    },
+    onError: (err) => notifyYouTubeActionError(err, t("channel.fullHistoryFailed")),
+  });
+
   const onUnsubscribe = async () => {
     const ok = await confirm({
       title: t("channel.unsubTitle"),
@@ -191,7 +207,14 @@ export default function ChannelPage({
     ch?.subscriber_count != null
       ? t("channel.subscribers", { formatted: formatViews(ch.subscriber_count) })
       : null,
-    ch?.video_count != null ? t("channel.videoCount", { count: ch.video_count }) : null,
+    // Show "stored / total" when we only hold a subset of a subscribed channel's uploads, so the
+    // gap between the browsable videos and YouTube's raw count is honest rather than looking like
+    // missing data (the "get full history" button pulls the rest).
+    ch?.video_count != null
+      ? ch.subscribed && !ch.backfill_done && ch.stored_videos < ch.video_count
+        ? t("channel.videoCountStored", { stored: ch.stored_videos, total: ch.video_count })
+        : t("channel.videoCount", { count: ch.video_count })
+      : null,
     ch?.total_view_count != null
       ? t("channel.totalViews", { formatted: formatViews(ch.total_view_count) })
       : null,
@@ -330,6 +353,27 @@ export default function ChannelPage({
                   <SlidersHorizontal className="w-4 h-4" />
                 </button>
               )}
+              {/* Only the recent subset is stored → offer to pull the channel's full back-catalogue.
+                Once queued (deep_requested) it shows as loading; hidden once the backfill is done. */}
+              {ch?.subscribed && !ch.backfill_done && !me.is_demo && (
+                <button
+                  onClick={() => !ch.deep_requested && deepBackfill.mutate()}
+                  disabled={ch.deep_requested || deepBackfill.isPending}
+                  title={
+                    ch.deep_requested ? t("channel.fullHistoryLoading") : t("channel.fullHistory")
+                  }
+                  className="inline-flex items-center gap-1.5 px-3 py-2 rounded-lg text-sm border border-border text-muted hover:text-accent hover:border-accent disabled:opacity-60 disabled:hover:text-muted disabled:hover:border-border transition"
+                >
+                  {ch.deep_requested ? (
+                    <Loader2 className="w-4 h-4 animate-spin" />
+                  ) : (
+                    <History className="w-4 h-4" />
+                  )}
+                  <span className="hidden sm:inline">
+                    {ch.deep_requested ? t("channel.fullHistoryLoading") : t("channel.fullHistory")}
+                  </span>
+                </button>
+              )}
               {!me.is_demo && (
                 <button
                   onClick={() => block.mutate()}

frontend/src/i18n/locales/en/channel.json

@@ -10,6 +10,7 @@
   "subscribers": "{{formatted}} subscribers",
   "videoCount_one": "{{count}} video",
   "videoCount_other": "{{count}} videos",
+  "videoCountStored": "{{stored}} / {{total}} videos",
   "totalViews": "{{formatted}} views",
   "joined": "Joined {{date}}",
   "loadingVideos": "Loading this channel's videos…",
@@ -24,5 +25,9 @@
   "language": "Language",
   "topics": "Topics",
   "keywords": "Keywords",
-  "showInFeed": "Show in my feed"
+  "showInFeed": "Show in my feed",
+  "fullHistory": "Full history",
+  "fullHistoryLoading": "Fetching history…",
+  "fullHistoryQueued": "Fetching this channel's full history — new videos will appear as they're found.",
+  "fullHistoryFailed": "Couldn't start the full-history fetch."
 }

frontend/src/i18n/locales/hu/channel.json

@@ -10,6 +10,7 @@
   "subscribers": "{{formatted}} feliratkozó",
   "videoCount_one": "{{count}} videó",
   "videoCount_other": "{{count}} videó",
+  "videoCountStored": "{{stored}} / {{total}} videó",
   "totalViews": "{{formatted}} megtekintés",
   "joined": "Csatlakozott: {{date}}",
   "loadingVideos": "A csatorna videóinak betöltése…",
@@ -24,5 +25,9 @@
   "language": "Nyelv",
   "topics": "Témák",
   "keywords": "Kulcsszavak",
-  "showInFeed": "Mutasd a hírfolyamomban"
+  "showInFeed": "Mutasd a hírfolyamomban",
+  "fullHistory": "Teljes előzmény",
+  "fullHistoryLoading": "Előzmény letöltése…",
+  "fullHistoryQueued": "A csatorna teljes előzményének letöltése elindult — az új videók feltűnnek, ahogy előkerülnek.",
+  "fullHistoryFailed": "Nem sikerült elindítani a teljes előzmény letöltését."
 }

frontend/src/lib/api.ts

@@ -136,6 +136,8 @@ export interface ChannelDetail {
   explored: boolean;
   blocked: boolean;
   stored_videos: number;
+  deep_requested: boolean;
+  backfill_done: boolean;
   from_explore: boolean;
   details_synced: boolean;
 }