fix(deferred): close frontend UI/UX tails from the hygiene sweep

- player YB2: keepalive pagehide beacon (api.saveProgressBeacon) so the resume
  position isn't lost on F5/close within 5s of the last checkpoint (mirrors Plex).
- player YB4: bound consecutive unplayable items in auto-advance so an
  auto-advancing/loop=all queue can't spin over a run of dead videos.
- downloads B6 (client): localise structured quota/edit errors centrally in
  api.req() via localizeDetail() + Intl.NumberFormat (fixes HU/DE + decimal sep);
  + 3-locale download error strings.
- channels FB1: focusChannelToken bump so re-clicking the same channel re-seeds
  the search box; FB2: syncSubs invalidates feed/feed-count (set can change now).
- config CB2: reseed the ConfigPanel draft on a key-set dataVersion + explicit
  post-save token, so a mid-edit refetch can't clobber an in-progress edit.
- config AB3 (UI): a blank allow_empty field stores "" instead of resetting.
- admin SB2/SC2: confirm + success toast on demo-whitelist remove and deny-invite
  (+ trilingual strings); SC1: disable only the acted-on row (pendingId), not all;
  SB3: pause the 1s scheduler countdown ticker while the tab is hidden.
- messages CT4: only invalidate conversations/unread when the incoming-message
  count actually changed, not on every 20s poll; MB3 (client): react to the live
  unread ping (onUnread → invalidate); MC3: extract e2ee installKey (setup/unlock);
  CC2: hoist POLL_MS to messaging.ts; MB4: document the reload-scoped socket.

frontend/src/components/ChatThread.tsx

@@ -6,12 +6,10 @@ import { api, HttpError, type Message, type MessageUser } from "../lib/api";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { relativeTime } from "../lib/format";
 import { notify } from "../lib/notifications";
-import { partnerPub, useKeyState } from "../lib/messaging";
+import { partnerPub, POLL_MS, useKeyState } from "../lib/messaging";
 import * as e2ee from "../lib/e2ee";
 import KeyGate from "./KeyGate";
 
-const POLL_MS = 20000; // safety net; live updates arrive over the WebSocket
-
 // The message list + composer for one conversation, shared by the full Messages page and the
 // floating dock window. Handles client-side decryption and encrypt-on-send; the surrounding
 // chrome (back button / minimize / close) is the caller's. Self-contained key gating: prompts
@@ -66,13 +64,20 @@ export default function ChatThread({
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [q.dataUpdatedAt, ready, isSystem, partnerId, t]);
 
-  // Opening / refreshing the thread marks incoming messages read, so clear the badges.
+  // Opening the thread (or a new incoming message arriving) marks messages read server-side, so
+  // refresh the badges — but ONLY when the incoming-message count actually changed, not on every
+  // 20s poll (which would needlessly refetch /conversations + /unread_count each tick).
+  const lastIncoming = useRef(-1);
   useEffect(() => {
-    if (q.dataUpdatedAt) {
+    if (!q.dataUpdatedAt) return;
+    const incoming = (q.data?.items ?? []).filter((m) => m.recipient_id === meId).length;
+    if (incoming !== lastIncoming.current) {
+      lastIncoming.current = incoming;
       qc.invalidateQueries({ queryKey: ["conversations"] });
       qc.invalidateQueries({ queryKey: ["message-unread"] });
     }
-  }, [q.dataUpdatedAt, qc]);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [q.dataUpdatedAt, meId, qc]);
 
   // Scroll to the newest message when the count changes (open / new message) — NOT on `plain`,
   // which gets a fresh object on every poll's decrypt pass and would yank a scrolled-up reader