fix(player): related marks survive, Restart restarts, and refused pages offer nothing to click

- Every state and Watch-later write goes through features/video/videoWrites,
  which marks the never-refetched lists (related lists, live searches) once
  the server has it; a contract test holds it. The Notification Center's
  undo, the feed's reset and the Watch-later toggles skipped it before.
- Confirmed marks are also kept apart (qk.videoMarks) and laid over the
  related rows: a Show more page landing later rebuilt them from the pages
  it read when it started, and dropped a mark made meanwhile.
- Restart on a related video starts at 0 (the session's stored position
  won before), and on the one already playing it seeks.
- The watched toggle remembers each video's mark: Back showed the opened
  video's launch-time state after a related one was marked.
- The help sheet leaves out the player's keys while a layer above it has
  them waiting.
- After a refusal a retry cannot answer, neither Show more (related) nor
  Load more (live search) is offered; a failed live-search page keeps the
  results already read and says why under them.
- The related cap message counts requests, as the cap does.

frontend/src/features/player/RelatedVideos.tsx

@@ -3,11 +3,18 @@ import { useTranslation } from "react-i18next";
 import { useInfiniteQuery, useQueryClient } from "@tanstack/react-query";
 import { CircleCheck } from "lucide-react";
 
-import { api, HttpError, type RelatedRegion, type Video, type VideoStatus } from "../../lib/api";
+import {
+  api,
+  HttpError,
+  refusalReason,
+  type RelatedRegion,
+  type Video,
+  type VideoStatus,
+} from "../../lib/api";
 import { qk } from "../../lib/queryKeys";
 import { nextPageOnClick } from "../../lib/nextPage";
 import { usePref, type UsePrefOptions } from "../../lib/usePref";
-import { patchRelated } from "../../lib/progressCache";
+import { useVideoMarks } from "../../lib/progressCache";
 import { notifyActionError } from "../../lib/actionErrors";
 import { Button } from "../../components/ui/Button";
 import SegmentedToggle from "../../components/ui/SegmentedToggle";
@@ -18,6 +25,7 @@ import Tooltip from "../../components/ui/Tooltip";
 import VideoCard from "../video/VideoCard";
 import { VideoMenu } from "../video/VideoMenu";
 import { announceVideoState } from "../video/stateNotice";
+import { writeVideoState, writeWatchLater } from "../video/videoWrites";
 
 /** Which list YouTube fills in — on the video's topic or with what trends in Hungary — is a mood,
  *  decided at the list, and the account keeps the last one (the owner's pick). */
@@ -33,9 +41,7 @@ const isSeen = (v: Video) => v.status === "watched" || v.status === "hidden";
 /** The refusals a retry cannot answer: the day's cap (tomorrow does), the feature turned off on
  *  this instance and the shared budget spent (the admin, or tomorrow). */
 const FINAL_REASONS = new Set(["related_daily_limit", "related_disabled", "quota"]);
-const isFinal = (e: unknown) =>
-  e instanceof HttpError &&
-  FINAL_REASONS.has((e.detailData as { reason?: string } | undefined)?.reason ?? "");
+const isFinal = (e: unknown) => FINAL_REASONS.has(refusalReason(e) ?? "");
 
 // A write not yet confirmed: its change shows at once, and leaves when the server answers.
 type Pending = { seq: number; id: string; change: Partial<Video> };
@@ -49,7 +55,8 @@ export function RelatedVideos({
   onWrite,
 }: {
   videoId: string;
-  onPlay: (v: Video, startAt: number) => void;
+  /** `startAt` null resumes the video where it was left; a number (Restart's 0) starts there. */
+  onPlay: (v: Video, startAt: number | null) => void;
   /** Each write this list makes, for the host's player session (see PlayerModal `onWrite`). */
   onWrite?: (write: Promise<unknown>) => void;
 }) {
@@ -83,11 +90,10 @@ export function RelatedVideos({
   const onState = (id: string, status: VideoStatus) => {
     const v = rows.find((x) => x.id === id);
     const seq = begin(id, { status });
-    const write = api.setState(id, status);
+    const write = writeVideoState(qc, id, status);
     onWrite?.(write);
     write
       .then(() => {
-        patchRelated(qc, id, { status });
         settle(seq);
         // Stale-mark the feed, as its own marks do: the video may be in it too.
         void qc.invalidateQueries({ queryKey: qk.feed(), refetchType: "none" });
@@ -101,11 +107,10 @@ export function RelatedVideos({
 
   const onToggleSave = (id: string, saved: boolean) => {
     const seq = begin(id, { saved });
-    const write = saved ? api.watchLaterAdd(id) : api.watchLaterRemove(id);
+    const write = writeWatchLater(qc, id, saved);
     onWrite?.(write);
     write
       .then(() => {
-        patchRelated(qc, id, { saved });
         settle(seq);
         void qc.invalidateQueries({ queryKey: qk.playlists() });
         void qc.invalidateQueries({ queryKey: qk.playlist() });
@@ -119,12 +124,15 @@ export function RelatedVideos({
       });
   };
 
-  const open = (v: Video, startAt?: number | null) => onPlay(v, startAt ?? v.position_seconds);
+  const open = (v: Video, startAt?: number | null) => onPlay(v, startAt ?? null);
   const menu = useContextMenu<Video>();
   const openId = menu.open ? menu.target?.id : undefined;
 
+  // What this session confirmed about a row (here or anywhere else), then what is on its way.
+  const marks = useVideoMarks();
   const rows = (query.data?.pages ?? [])
     .flatMap((p) => p.items)
+    .map((v) => (marks[v.id] ? { ...v, ...marks[v.id] } : v))
     .map((v) => pending.reduce((acc, w) => (w.id === v.id ? { ...acc, ...w.change } : acc), v))
     .filter((v) => !isSeen(v));
   const followed = new Set(
@@ -139,7 +147,8 @@ export function RelatedVideos({
         : null;
   // A refused page is the one to try again: with pages loaded, a refetch started over from the first
   // (another scrape and another slot) instead of asking for the page that failed.
-  const retry = isFinal(query.error)
+  const final = isFinal(query.error);
+  const retry = final
     ? undefined
     : query.data?.pages.length
       ? () => void query.fetchNextPage(nextPageOnClick(query.isFetchingNextPage))
@@ -203,7 +212,8 @@ export function RelatedVideos({
               />
             ))}
           </NavGrid>
-          {query.hasNextPage && (
+          {/* Show more is the same request a Retry makes: refused for good, neither is offered. */}
+          {query.hasNextPage && !final && (
             <div className="mt-3 flex justify-center">
               <Button
                 variant="outline"