diff --git a/backend/app/routes/feed.py b/backend/app/routes/feed.py
index 2fc5044..2917244 100644
--- a/backend/app/routes/feed.py
+++ b/backend/app/routes/feed.py
@@ -4,9 +4,12 @@ from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy import Select, and_, false, func, or_, select
 from sqlalchemy.orm import Session, aliased
 
+from app import quota
 from app.auth import current_user
 from app.db import get_db
 from app.models import Channel, ChannelTag, Subscription, Tag, User, Video, VideoState
+from app.sync.videos import parse_iso8601_duration
+from app.youtube.client import YouTubeClient, YouTubeError
 
 router = APIRouter(prefix="/api", tags=["feed"])
 
@@ -287,3 +290,57 @@ def set_video_state(
     row.watched_at = datetime.now(timezone.utc) if status == "watched" else row.watched_at
     db.commit()
     return {"video_id": video_id, "status": status}
+
+
+@router.get("/videos/{video_id}")
+def get_video_detail(
+    video_id: str,
+    user: User = Depends(current_user),
+    db: Session = Depends(get_db),
+) -> dict:
+    """On-demand detail (description, like count) — kept out of the feed list payload
+    so the feed stays lean; fetched lazily, e.g. for the title hover popover.
+
+    Videos we already store are served from the DB for free. A video that isn't in
+    our DB (e.g. a YouTube link inside another video's description that the in-app
+    player navigated to) is resolved via the YouTube API (videos.list, 1 unit,
+    attributed to the requesting user)."""
+    v = db.get(Video, video_id)
+    if v is not None:
+        return {
+            "id": v.id,
+            "description": v.description,
+            "like_count": v.like_count,
+            "in_db": True,
+            "channel_id": v.channel_id,
+            "channel_title": v.channel.title if v.channel else None,
+            "published_at": v.published_at.isoformat() if v.published_at else None,
+            "view_count": v.view_count,
+            "duration_seconds": v.duration_seconds,
+        }
+
+    try:
+        with quota.attribute(user.id, "video_lookup"), YouTubeClient(db, user) as yt:
+            items = yt.get_videos([video_id])
+    except YouTubeError as exc:
+        raise HTTPException(status_code=502, detail=f"YouTube lookup failed: {exc}")
+    if not items:
+        raise HTTPException(status_code=404, detail="Unknown video")
+
+    snippet = items[0].get("snippet", {})
+    stats = items[0].get("statistics", {})
+    likes = stats.get("likeCount")
+    views = stats.get("viewCount")
+    return {
+        "id": video_id,
+        "description": snippet.get("description"),
+        "like_count": int(likes) if likes is not None else None,
+        "in_db": False,
+        "channel_id": snippet.get("channelId"),
+        "channel_title": snippet.get("channelTitle"),
+        "published_at": snippet.get("publishedAt"),
+        "view_count": int(views) if views is not None else None,
+        "duration_seconds": parse_iso8601_duration(
+            items[0].get("contentDetails", {}).get("duration")
+        ),
+    }
diff --git a/frontend/src/components/Feed.tsx b/frontend/src/components/Feed.tsx
index 747149b..2652be3 100644
--- a/frontend/src/components/Feed.tsx
+++ b/frontend/src/components/Feed.tsx
@@ -3,6 +3,7 @@ import { useInfiniteQuery, useQuery, useQueryClient } from "@tanstack/react-quer
 import { api, type FeedFilters, type Video } from "../lib/api";
 import { notify } from "../lib/notifications";
 import VideoCard from "./VideoCard";
+import PlayerModal from "./PlayerModal";
 
 const PAGE = 60;
 
@@ -31,6 +32,7 @@ export default function Feed({
   view: "grid" | "list";
 }) {
   const [overrides, setOverrides] = useState<Record<string, string>>({});
+  const [activeVideo, setActiveVideo] = useState<Video | null>(null);
   const qc = useQueryClient();
 
   const query = useInfiniteQuery({
@@ -40,7 +42,12 @@ export default function Feed({
     getNextPageParam: (last) => (last.has_more ? last.offset + last.limit : undefined),
   });
 
+  // Drop optimistic status overrides when filters change OR fresh server data
+  // arrives — after a refetch the server is authoritative, so a stale override
+  // (e.g. a video reverted to "new" from the notification center) won't keep it
+  // filtered out of the current view.
   useEffect(() => setOverrides({}), [filters]);
+  useEffect(() => setOverrides({}), [query.dataUpdatedAt]);
 
   const countQuery = useQuery({
     queryKey: ["feed-count", filters],
@@ -85,6 +92,13 @@ export default function Feed({
           channelName: v?.channel_title ?? "",
         },
       });
+    } else if (status === "watched") {
+      const v = (query.data?.pages ?? []).flatMap((p) => p.items).find((x) => x.id === id);
+      notify({
+        message: v?.title ? `Marked watched “${v.title}”` : "Marked watched",
+        action: { label: "Unwatch", onClick: () => onState(id, "new") },
+        meta: { kind: "video-watched", videoId: id, title: v?.title ?? "this video" },
+      });
     }
   }
 
@@ -118,6 +132,7 @@ export default function Feed({
               view="grid"
               onState={onState}
               onChannelFilter={onChannelFilter}
+              onOpen={setActiveVideo}
             />
           ))}
         </div>
@@ -130,10 +145,18 @@ export default function Feed({
               view="list"
               onState={onState}
               onChannelFilter={onChannelFilter}
+              onOpen={setActiveVideo}
             />
           ))}
         </div>
       )}
+      {activeVideo && (
+        <PlayerModal
+          video={activeVideo}
+          onClose={() => setActiveVideo(null)}
+          onState={onState}
+        />
+      )}
       <div ref={sentinel} className="h-10" />
       {isFetchingNextPage && (
         <div className="text-center text-muted py-4">Loading more…</div>
diff --git a/frontend/src/components/NotificationCenter.tsx b/frontend/src/components/NotificationCenter.tsx
index 5ba96e4..4603218 100644
--- a/frontend/src/components/NotificationCenter.tsx
+++ b/frontend/src/components/NotificationCenter.tsx
@@ -1,6 +1,6 @@
 import { useEffect, useRef, useState, useSyncExternalStore } from "react";
 import { useQueryClient } from "@tanstack/react-query";
-import { Bell, Eye, Search, Trash2 } from "lucide-react";
+import { Bell, Eye, RotateCcw, Search, Trash2 } from "lucide-react";
 import { api, type FeedFilters } from "../lib/api";
 import {
   clearAll,
@@ -10,7 +10,8 @@ import {
   markAllRead,
   notify,
   subscribe,
-  type NotifMeta,
+  type VideoHiddenMeta,
+  type VideoWatchedMeta,
 } from "../lib/notifications";
 import { LEVEL_STYLE } from "./Toaster";
 
@@ -53,7 +54,7 @@ export default function NotificationCenter({
     if (open) markAllRead();
   }, [open, notifications.length]);
 
-  function locateHidden(meta: NotifMeta) {
+  function locateHidden(meta: VideoHiddenMeta) {
     setFilters({
       ...filters,
       show: "hidden",
@@ -63,13 +64,13 @@ export default function NotificationCenter({
     setOpen(false);
   }
 
-  function unhide(meta: NotifMeta) {
+  function revertState(meta: VideoHiddenMeta | VideoWatchedMeta, verb: string) {
     api
       .setState(meta.videoId, "new")
       .then(() => {
         qc.invalidateQueries({ queryKey: ["feed"] });
         qc.invalidateQueries({ queryKey: ["feed-count"] });
-        notify({ level: "success", message: `Unhidden “${meta.title}”` });
+        notify({ level: "success", message: `${verb} “${meta.title}”` });
       })
       .catch(() => {});
   }
@@ -113,6 +114,7 @@ export default function NotificationCenter({
                 const { icon: Icon, color } = LEVEL_STYLE[n.level];
                 const needsAction = n.requiresInteraction && !n.dismissed;
                 const hidden = n.meta?.kind === "video-hidden" ? n.meta : null;
+                const watched = n.meta?.kind === "video-watched" ? n.meta : null;
                 return (
                   <div
                     key={n.id}
@@ -143,13 +145,23 @@ export default function NotificationCenter({
                             Find in feed
                           </button>
                           <button
-                            onClick={() => unhide(hidden)}
+                            onClick={() => revertState(hidden, "Unhidden")}
                             className="flex items-center gap-1 text-accent text-sm font-semibold hover:underline"
                           >
                             <Eye className="w-3.5 h-3.5" />
                             Unhide
                           </button>
                         </div>
+                      ) : watched ? (
+                        <div className="flex items-center gap-3 mt-1">
+                          <button
+                            onClick={() => revertState(watched, "Unwatched")}
+                            className="flex items-center gap-1 text-accent text-sm font-semibold hover:underline"
+                          >
+                            <RotateCcw className="w-3.5 h-3.5" />
+                            Unwatch
+                          </button>
+                        </div>
                       ) : (
                         n.action &&
                         !n.dismissed && (
diff --git a/frontend/src/components/PlayerModal.tsx b/frontend/src/components/PlayerModal.tsx
new file mode 100644
index 0000000..05c4083
--- /dev/null
+++ b/frontend/src/components/PlayerModal.tsx
@@ -0,0 +1,533 @@
+import { useEffect, useRef, useState, type ReactNode } from "react";
+import { createPortal } from "react-dom";
+import { useQuery } from "@tanstack/react-query";
+import { ArrowLeft, Check, CheckCheck, X } from "lucide-react";
+import { api, type Video } from "../lib/api";
+import { formatDuration, formatViews, relativeTime } from "../lib/format";
+
+// Turn a description into clickable nodes:
+//  - bare timestamps (mm:ss / hh:mm:ss) → seek the inline player
+//  - a YouTube link to the *current* video → seek (to its t= if any)
+//  - a YouTube link to *another* video → load it in the inline player
+//  - emails → mailto:, hashtags → YouTube's hashtag page, other URLs → new tab
+const URL_RE = /(https?:\/\/[^\s<>]+)/g;
+// One pass over plain text for the three inline token kinds (email | hashtag | timestamp).
+const INLINE_RE =
+  /([A-Za-z0-9._%+-]+@[A-Za-z0-9-]+\.[A-Za-z0-9.-]+)|(#[\p{L}\p{N}_]+)|(\b(?:\d{1,2}:)?\d{1,2}:\d{2}\b)/gu;
+
+function tsToSeconds(ts: string): number {
+  const parts = ts.split(":").map((n) => parseInt(n, 10));
+  return parts.length === 3
+    ? parts[0] * 3600 + parts[1] * 60 + parts[2]
+    : parts[0] * 60 + parts[1];
+}
+
+// Parse a YouTube `t`/`start` param: "90", "90s", or "1h2m3s".
+function parseStart(t: string | null): number | null {
+  if (!t) return null;
+  if (/^\d+$/.test(t)) return parseInt(t, 10) || null;
+  const m = t.match(/^(?:(\d+)h)?(?:(\d+)m)?(?:(\d+)s)?$/);
+  if (!m) return null;
+  const total =
+    parseInt(m[1] || "0", 10) * 3600 +
+    parseInt(m[2] || "0", 10) * 60 +
+    parseInt(m[3] || "0", 10);
+  return total || null;
+}
+
+// Extract a video id (+ optional start) from a YouTube URL, else null.
+function parseYouTube(url: string): { id: string; start: number | null } | null {
+  let u: URL;
+  try {
+    u = new URL(url);
+  } catch {
+    return null;
+  }
+  const host = u.hostname.replace(/^www\./, "");
+  let id: string | null = null;
+  if (host === "youtu.be") {
+    id = u.pathname.slice(1) || null;
+  } else if (host === "youtube.com" || host === "m.youtube.com" || host === "music.youtube.com") {
+    if (u.pathname === "/watch") id = u.searchParams.get("v");
+    else {
+      const m = u.pathname.match(/^\/(?:shorts|embed|live)\/([^/?#]+)/);
+      if (m) id = m[1];
+    }
+  }
+  if (!id) return null;
+  return { id, start: parseStart(u.searchParams.get("t") || u.searchParams.get("start")) };
+}
+
+function renderDescription(
+  text: string,
+  opts: {
+    currentId: string;
+    onSeek: (seconds: number) => void;
+    onLoadVideo: (id: string, start: number | null) => void;
+  }
+): ReactNode[] {
+  const out: ReactNode[] = [];
+  let key = 0;
+  const linkCls = "text-accent hover:underline break-all";
+  // Tidy YouTube descriptions: drop trailing spaces and remove blank lines entirely
+  // (they're just noise in the popover), keeping single line breaks.
+  const clean = text.replace(/[ \t]+\n/g, "\n").replace(/\n{2,}/g, "\n").trim();
+  for (const chunk of clean.split(URL_RE)) {
+    if (/^https?:\/\//.test(chunk)) {
+      const href = chunk.replace(/[.,;:!?)\]]+$/, "");
+      const yt = parseYouTube(href);
+      if (yt) {
+        const sameVideo = yt.id === opts.currentId;
+        out.push(
+          <button
+            key={key++}
+            onClick={() =>
+              sameVideo ? opts.onSeek(yt.start ?? 0) : opts.onLoadVideo(yt.id, yt.start)
+            }
+            className={linkCls}
+            title={sameVideo ? "Jump to this time" : "Play in the in-app player"}
+          >
+            {href}
+          </button>
+        );
+      } else {
+        out.push(
+          <a key={key++} href={href} target="_blank" rel="noreferrer" className={linkCls}>
+            {href}
+          </a>
+        );
+      }
+      continue;
+    }
+    // Plain text: pull out emails, hashtags and bare timestamps.
+    INLINE_RE.lastIndex = 0;
+    let last = 0;
+    let m: RegExpExecArray | null;
+    while ((m = INLINE_RE.exec(chunk))) {
+      if (m.index > last) out.push(<span key={key++}>{chunk.slice(last, m.index)}</span>);
+      if (m[1]) {
+        // Email — trim trailing punctuation the domain rule may have swallowed.
+        const email = m[1].replace(/[.,;:]+$/, "");
+        out.push(
+          <a key={key++} href={`mailto:${email}`} className={linkCls}>
+            {email}
+          </a>
+        );
+        if (m[1].length > email.length) out.push(<span key={key++}>{m[1].slice(email.length)}</span>);
+      } else if (m[2]) {
+        // Hashtag → YouTube's hashtag feed (mirrors native YouTube behavior).
+        const tag = m[2].slice(1);
+        out.push(
+          <a
+            key={key++}
+            href={`https://www.youtube.com/hashtag/${encodeURIComponent(tag)}`}
+            target="_blank"
+            rel="noreferrer"
+            className={linkCls}
+          >
+            {m[2]}
+          </a>
+        );
+      } else {
+        const ts = m[3];
+        out.push(
+          <button
+            key={key++}
+            onClick={() => opts.onSeek(tsToSeconds(ts))}
+            className="text-accent hover:underline"
+          >
+            {ts}
+          </button>
+        );
+      }
+      last = m.index + m[0].length;
+    }
+    if (last < chunk.length) out.push(<span key={key++}>{chunk.slice(last)}</span>);
+  }
+  return out;
+}
+
+// Experiment (branch experiment/inline-player): play the video in-app via the
+// YouTube IFrame Player API (not a bare embed) so we can read playback position
+// and resume where the user left off. The modal closes via the in-card Close
+// button, the backdrop, or ESC (ESC only while focus is on our page, not inside
+// the cross-origin player iframe — a browser security boundary we can't cross).
+
+// How close to the end (seconds) counts as "finished" → auto-mark watched.
+const FINISH_MARGIN = 10;
+
+// --- IFrame Player API loader (singleton) ---
+let apiPromise: Promise<any> | null = null;
+function loadYouTubeApi(): Promise<any> {
+  if (apiPromise) return apiPromise;
+  apiPromise = new Promise((resolve) => {
+    const w = window as any;
+    if (w.YT && w.YT.Player) return resolve(w.YT);
+    const prev = w.onYouTubeIframeAPIReady;
+    w.onYouTubeIframeAPIReady = () => {
+      if (typeof prev === "function") prev();
+      resolve(w.YT);
+    };
+    const tag = document.createElement("script");
+    tag.src = "https://www.youtube.com/iframe_api";
+    document.head.appendChild(tag);
+  });
+  return apiPromise;
+}
+
+// --- Per-video resume position, persisted in localStorage so it survives a refresh ---
+const posKey = (id: string) => `subfeed:player-pos:${id}`;
+function savePos(id: string, seconds: number, duration: number): void {
+  // Don't store trivially-early or near-finished positions (start fresh next time).
+  if (!Number.isFinite(seconds) || seconds < 5 || (duration > 0 && seconds > duration - FINISH_MARGIN)) {
+    localStorage.removeItem(posKey(id));
+    return;
+  }
+  localStorage.setItem(posKey(id), String(Math.floor(seconds)));
+}
+function loadPos(id: string): number {
+  const v = localStorage.getItem(posKey(id));
+  const n = v ? parseInt(v, 10) : 0;
+  return Number.isFinite(n) && n > 0 ? n : 0;
+}
+
+export default function PlayerModal({
+  video,
+  onClose,
+  onState,
+}: {
+  video: Video;
+  onClose: () => void;
+  onState: (id: string, status: string) => void;
+}) {
+  const mountRef = useRef<HTMLDivElement | null>(null);
+  const playerRef = useRef<any>(null);
+  const autoMarkedRef = useRef(false);
+
+  // The player can navigate to other videos (YouTube links in a description). The
+  // currently-playing id may differ from the feed video we opened with.
+  const [currentVideoId, setCurrentVideoId] = useState(video.id);
+  const currentIdRef = useRef(video.id);
+  const navigated = currentVideoId !== video.id;
+  // Title/author of a navigated-to video, read from the player (free, no API call).
+  const [liveData, setLiveData] = useState<{ title?: string; author?: string } | null>(null);
+
+  const loadVideo = (id: string, start: number | null) => {
+    const p = playerRef.current;
+    if (!p || typeof p.loadVideoById !== "function") return;
+    const startSeconds = start != null ? start : loadPos(id);
+    p.loadVideoById({ videoId: id, startSeconds: startSeconds || 0 });
+    currentIdRef.current = id;
+    setCurrentVideoId(id);
+    setLiveData(null);
+  };
+
+  // Local mirror of watch status so the toggle reacts instantly; changes are
+  // propagated to the feed (and server) via onState.
+  const [status, setStatus] = useState(video.status);
+  const watched = status === "watched";
+  const setWatched = (on: boolean) => {
+    const next = on ? "watched" : "new";
+    setStatus(next);
+    onState(video.id, next);
+  };
+
+  const seekTo = (seconds: number) => {
+    const p = playerRef.current;
+    if (p && typeof p.seekTo === "function") {
+      p.seekTo(seconds, true);
+      p.playVideo?.();
+    }
+  };
+
+  // Lazy description (fetched only when the title is hovered). The popover is
+  // portaled to <body> with fixed positioning so the modal card's overflow-y-auto
+  // can't clip it. A small close grace lets the mouse travel title → popover.
+  const [showDesc, setShowDesc] = useState(false);
+  // `bottom` anchors the popover just above the title so it grows upward (over the
+  // player) instead of downward off-screen / behind the OS taskbar.
+  const [descRect, setDescRect] = useState<{ left: number; bottom: number; width: number } | null>(
+    null
+  );
+  const titleRef = useRef<HTMLSpanElement | null>(null);
+  const closeTimer = useRef<number | undefined>(undefined);
+  const openDesc = () => {
+    window.clearTimeout(closeTimer.current);
+    const el = titleRef.current;
+    if (el) {
+      const r = el.getBoundingClientRect();
+      const width = Math.min(560, window.innerWidth - 32);
+      const left = Math.max(16, Math.min(r.left, window.innerWidth - width - 16));
+      setDescRect({ left, bottom: window.innerHeight - r.top + 8, width });
+    }
+    setShowDesc(true);
+  };
+  const scheduleCloseDesc = () => {
+    closeTimer.current = window.setTimeout(() => setShowDesc(false), 150);
+  };
+  const detail = useQuery({
+    queryKey: ["video-detail", currentVideoId],
+    queryFn: () => api.videoDetail(currentVideoId),
+    // On hover (for the description) and eagerly when navigated, so we can link the
+    // linked video's channel. Both share the one cached result.
+    enabled: showDesc || navigated,
+    staleTime: 5 * 60_000,
+  });
+
+  // ESC + background scroll lock.
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === "Escape") onClose();
+    };
+    window.addEventListener("keydown", onKey);
+    const prevOverflow = document.body.style.overflow;
+    document.body.style.overflow = "hidden";
+    return () => {
+      window.removeEventListener("keydown", onKey);
+      document.body.style.overflow = prevOverflow;
+      window.clearTimeout(closeTimer.current);
+    };
+  }, [onClose]);
+
+  // Create the player, resume from the saved position, persist progress, and
+  // auto-mark watched once playback reaches the end.
+  useEffect(() => {
+    let cancelled = false;
+    const id = video.id;
+
+    // Auto-watch only applies to the feed video we opened with — not to other
+    // videos the player navigated to via description links.
+    const maybeAutoWatch = (current: number, duration: number) => {
+      if (autoMarkedRef.current || duration <= 0 || currentIdRef.current !== id) return;
+      if (current > duration - FINISH_MARGIN) {
+        autoMarkedRef.current = true;
+        setWatched(true);
+      }
+    };
+    const persist = () => {
+      const p = playerRef.current;
+      if (!p || typeof p.getCurrentTime !== "function") return;
+      try {
+        const cur = p.getCurrentTime();
+        const dur = typeof p.getDuration === "function" ? p.getDuration() : 0;
+        maybeAutoWatch(cur, dur);
+        savePos(currentIdRef.current, cur, dur); // key progress by what's actually playing
+      } catch {
+        /* player may be tearing down */
+      }
+    };
+
+    loadYouTubeApi().then((YT) => {
+      if (cancelled || !mountRef.current) return;
+      playerRef.current = new YT.Player(mountRef.current, {
+        width: "100%",
+        height: "100%",
+        videoId: id,
+        playerVars: {
+          autoplay: 1,
+          start: loadPos(id) || undefined,
+          rel: 0, // limit "related" to the same channel (full removal is no longer possible)
+          enablejsapi: 1,
+          origin: window.location.origin,
+          playsinline: 1,
+        },
+        events: {
+          onStateChange: (e: any) => {
+            // 1 === playing → sync the navigated-to video's title/author for display.
+            if (e?.data === 1) {
+              const p = playerRef.current;
+              const d = p && typeof p.getVideoData === "function" ? p.getVideoData() : null;
+              if (d) setLiveData({ title: d.title, author: d.author });
+            }
+            // 0 === ended → mark watched (guarded to the feed video inside maybeAutoWatch).
+            if (e?.data === 0 && !autoMarkedRef.current && currentIdRef.current === id) {
+              autoMarkedRef.current = true;
+              setWatched(true);
+            }
+          },
+        },
+      });
+    });
+
+    // Periodic checkpoint so progress (and auto-watch) survive a crash/refresh.
+    const timer = window.setInterval(persist, 5000);
+
+    return () => {
+      cancelled = true;
+      window.clearInterval(timer);
+      persist();
+      const p = playerRef.current;
+      if (p && typeof p.destroy === "function") {
+        try {
+          p.destroy();
+        } catch {
+          /* ignore */
+        }
+      }
+      playerRef.current = null;
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [video.id]);
+
+  return (
+    <div
+      className="fixed inset-0 z-50 flex items-center justify-center p-4 sm:p-6 bg-black/80 backdrop-blur-sm"
+      onClick={onClose}
+      role="dialog"
+      aria-modal="true"
+    >
+      <div
+        className="glass-card relative w-full max-w-4xl max-h-full overflow-y-auto rounded-2xl shadow-2xl"
+        onClick={(e) => e.stopPropagation()}
+      >
+        <div className="aspect-video w-full bg-black rounded-t-2xl overflow-hidden">
+          <div ref={mountRef} className="w-full h-full" />
+        </div>
+
+        <div className="p-4 sm:p-5">
+          {/* Title row — title (with hover description) on the left, Close on the right. */}
+          <div className="flex items-start gap-3">
+            <h2 className="min-w-0 flex-1 text-lg font-semibold leading-snug">
+              {/* Hover target is the text itself (inline), not the whole row. */}
+              <span
+                ref={titleRef}
+                className="cursor-default"
+                onMouseEnter={openDesc}
+                onMouseLeave={scheduleCloseDesc}
+              >
+                {navigated ? liveData?.title ?? "Loading…" : video.title}
+              </span>
+            </h2>
+            {navigated && (
+              <button
+                onClick={() => loadVideo(video.id, null)}
+                title="Back to the original video"
+                className="shrink-0 inline-flex items-center gap-1.5 text-sm px-3 py-1.5 rounded-lg text-muted hover:text-fg hover:bg-surface transition"
+              >
+                <ArrowLeft className="w-4 h-4" />
+                Back
+              </button>
+            )}
+            {showDesc &&
+              descRect &&
+              createPortal(
+                <div
+                  className="fixed z-[60] bg-surface border border-border rounded-xl shadow-2xl p-4"
+                  style={{
+                    left: descRect.left,
+                    bottom: descRect.bottom,
+                    width: descRect.width,
+                  }}
+                  onMouseEnter={openDesc}
+                  onMouseLeave={scheduleCloseDesc}
+                >
+                  <div className="text-xs uppercase tracking-wide text-muted mb-2">
+                    Description
+                  </div>
+                  {detail.isLoading ? (
+                    <div className="text-sm text-muted">Loading…</div>
+                  ) : detail.data?.description ? (
+                    <div className="text-sm whitespace-pre-wrap break-words max-h-64 overflow-y-auto leading-relaxed">
+                      {renderDescription(detail.data.description, {
+                        currentId: currentVideoId,
+                        onSeek: seekTo,
+                        onLoadVideo: loadVideo,
+                      })}
+                    </div>
+                  ) : (
+                    <div className="text-sm text-muted">No description.</div>
+                  )}
+                </div>,
+                document.body
+              )}
+            <button
+              onClick={onClose}
+              title="Close (Esc)"
+              className="shrink-0 inline-flex items-center gap-1.5 text-sm px-3 py-1.5 rounded-lg text-muted hover:text-fg hover:bg-surface transition"
+            >
+              Close
+              <X className="w-4 h-4" />
+            </button>
+          </div>
+
+          {/* Channel + meta on one line, with the watched toggle pushed to the right.
+              When navigated to a linked video we only have its author (from the player),
+              so we show that as plain text and hide feed-video-specific bits. */}
+          <div className="flex items-center gap-3 mt-3">
+            {!navigated && video.channel_thumbnail && (
+              <img
+                src={video.channel_thumbnail}
+                alt=""
+                className="w-9 h-9 rounded-full shrink-0"
+              />
+            )}
+            {navigated ? (
+              detail.data?.channel_id ? (
+                <a
+                  href={`https://www.youtube.com/channel/${detail.data.channel_id}`}
+                  target="_blank"
+                  rel="noreferrer"
+                  className="font-medium hover:text-accent shrink-0"
+                >
+                  {liveData?.author ?? detail.data.channel_title ?? "Channel"}
+                </a>
+              ) : (
+                <span className="font-medium shrink-0">{liveData?.author ?? ""}</span>
+              )
+            ) : (
+              <a
+                href={video.channel_url}
+                target="_blank"
+                rel="noreferrer"
+                className="font-medium hover:text-accent shrink-0"
+              >
+                {video.channel_title}
+              </a>
+            )}
+            {!navigated ? (
+              <div className="flex flex-wrap items-center gap-x-2 gap-y-0.5 text-sm text-muted min-w-0">
+                {video.view_count != null && <span>· {formatViews(video.view_count)} views</span>}
+                <span>· {relativeTime(video.published_at)}</span>
+                {video.duration_seconds != null && (
+                  <span>· {formatDuration(video.duration_seconds)}</span>
+                )}
+                {video.live_status === "was_live" && (
+                  <span className="bg-accent text-accent-fg text-[10px] font-semibold uppercase tracking-wide px-1.5 py-0.5 rounded">
+                    stream
+                  </span>
+                )}
+              </div>
+            ) : (
+              // Linked video's stats come from the (already-fetched) video detail.
+              <div className="flex flex-wrap items-center gap-x-2 gap-y-0.5 text-sm text-muted min-w-0">
+                {detail.data?.view_count != null && (
+                  <span>· {formatViews(detail.data.view_count)} views</span>
+                )}
+                {detail.data?.published_at && <span>· {relativeTime(detail.data.published_at)}</span>}
+                {detail.data?.duration_seconds != null && (
+                  <span>· {formatDuration(detail.data.duration_seconds)}</span>
+                )}
+              </div>
+            )}
+
+            {!navigated && (
+              <button
+                onClick={() => setWatched(!watched)}
+                title={watched ? "Watched — click to unmark" : "Mark watched"}
+                className={
+                  "ml-auto shrink-0 inline-flex items-center gap-1.5 text-sm px-3 py-1.5 rounded-lg transition " +
+                  (watched
+                    ? "bg-accent text-accent-fg shadow-sm hover:opacity-90"
+                    : "text-muted hover:text-fg hover:bg-surface border border-border")
+                }
+              >
+                {watched ? <CheckCheck className="w-4 h-4" /> : <Check className="w-4 h-4" />}
+                {watched ? "Watched" : "Mark watched"}
+              </button>
+            )}
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/components/VideoCard.tsx b/frontend/src/components/VideoCard.tsx
index 8a4f7d5..c04aae6 100644
--- a/frontend/src/components/VideoCard.tsx
+++ b/frontend/src/components/VideoCard.tsx
@@ -1,4 +1,4 @@
-import { Bookmark, Check, Eye, EyeOff, ListFilter } from "lucide-react";
+import { Bookmark, Check, CheckCheck, Eye, EyeOff, ListFilter } from "lucide-react";
 import clsx from "clsx";
 import type { Video } from "../lib/api";
 import { formatDuration, formatViews, relativeTime } from "../lib/format";
@@ -21,20 +21,24 @@ function Actions({
     <div className="flex gap-1 opacity-0 group-hover:opacity-100 transition">
       <button
         onClick={act("watched")}
-        title="Mark watched"
+        title={video.status === "watched" ? "Watched — click to unmark" : "Mark watched"}
         className={clsx(
           "p-1.5 rounded-md hover:bg-surface text-muted hover:text-fg",
           video.status === "watched" && "text-accent"
         )}
       >
-        <Check className="w-4 h-4" />
+        {video.status === "watched" ? (
+          <CheckCheck className="w-4 h-4" />
+        ) : (
+          <Check className="w-4 h-4" />
+        )}
       </button>
       <button
         onClick={act("saved")}
-        title="Save for later"
+        title={video.status === "saved" ? "Saved — click to remove" : "Save for later"}
         className={clsx(
           "p-1.5 rounded-md hover:bg-surface text-muted hover:text-fg",
-          video.status === "saved" && "text-accent"
+          video.status === "saved" && "fill-current text-accent"
         )}
       >
         <Bookmark className="w-4 h-4" />
@@ -70,13 +74,33 @@ function Actions({
   );
 }
 
-function Thumb({ video, className }: { video: Video; className?: string }) {
+// Plain left-click opens the in-app player (the experiment); Ctrl/Cmd/middle-click
+// keep the native "open youtube.com in a new tab" behavior via the underlying href.
+function openInApp(
+  e: React.MouseEvent,
+  video: Video,
+  onOpen?: (v: Video) => void
+): void {
+  if (!onOpen || e.metaKey || e.ctrlKey || e.shiftKey || e.altKey || e.button !== 0) return;
+  e.preventDefault();
+  onOpen(video);
+}
+
+function Thumb({
+  video,
+  className,
+  onOpen,
+}: {
+  video: Video;
+  className?: string;
+  onOpen?: (v: Video) => void;
+}) {
   return (
     <a
       href={video.watch_url}
       target="_blank"
       rel="noreferrer"
-      onClick={() => video.status === "new" && undefined}
+      onClick={(e) => openInApp(e, video, onOpen)}
       className={clsx(
         "block relative rounded-xl overflow-hidden bg-surface border border-border shadow-md group-hover:shadow-2xl transition-shadow",
         className
@@ -116,11 +140,13 @@ export default function VideoCard({
   view,
   onState,
   onChannelFilter,
+  onOpen,
 }: {
   video: Video;
   view: "grid" | "list";
   onState: (id: string, status: string) => void;
   onChannelFilter?: (channelId: string, channelName: string) => void;
+  onOpen?: (v: Video) => void;
 }) {
   const watched = video.status === "watched";
   const meta = (
@@ -134,6 +160,7 @@ export default function VideoCard({
       href={video.watch_url}
       target="_blank"
       rel="noreferrer"
+      onClick={(e) => openInApp(e, video, onOpen)}
       className="font-medium leading-snug line-clamp-2 hover:text-accent"
     >
       {video.title}
@@ -148,7 +175,7 @@ export default function VideoCard({
           watched && "opacity-55"
         )}
       >
-        <Thumb video={video} className="w-44 aspect-video shrink-0" />
+        <Thumb video={video} className="w-44 aspect-video shrink-0" onOpen={onOpen} />
         <div className="min-w-0 flex-1">
           {title}
           <a
@@ -174,7 +201,7 @@ export default function VideoCard({
         watched && "opacity-55"
       )}
     >
-      <Thumb video={video} className="aspect-video" />
+      <Thumb video={video} className="aspect-video" onOpen={onOpen} />
       <div className="flex gap-3 mt-2.5 px-0.5 pb-0.5">
         {video.channel_thumbnail && (
           <img
diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index 5043300..fee444c 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -47,6 +47,18 @@ export interface Video {
   watch_url: string;
 }
 
+export interface VideoDetail {
+  id: string;
+  description: string | null;
+  like_count: number | null;
+  in_db: boolean;
+  channel_id: string | null;
+  channel_title: string | null;
+  published_at: string | null;
+  view_count: number | null;
+  duration_seconds: number | null;
+}
+
 export interface FeedResponse {
   items: Video[];
   has_more: boolean;
@@ -214,6 +226,7 @@ export const api = {
     req(`/api/feed/count?${feedQuery(f, 0, 0)}`),
   setState: (id: string, status: string) =>
     req(`/api/videos/${id}/state`, { method: "POST", body: JSON.stringify({ status }) }),
+  videoDetail: (id: string): Promise<VideoDetail> => req(`/api/videos/${id}`),
   pauseSync: () => req("/api/sync/pause", { method: "POST" }),
   resumeSync: () => req("/api/sync/resume", { method: "POST" }),
   savePrefs: (p: Record<string, any>) =>
diff --git a/frontend/src/lib/notifications.ts b/frontend/src/lib/notifications.ts
index f131d39..bf8dd27 100644
--- a/frontend/src/lib/notifications.ts
+++ b/frontend/src/lib/notifications.ts
@@ -12,13 +12,19 @@ export interface NotifAction {
 
 // Structured payload that lets the Notification Center offer in-app actions even
 // after a reload (when live `action` callbacks are gone).
-export type NotifMeta = {
+export type VideoHiddenMeta = {
   kind: "video-hidden";
   videoId: string;
   title: string;
   channelId: string;
   channelName: string;
 };
+export type VideoWatchedMeta = {
+  kind: "video-watched";
+  videoId: string;
+  title: string;
+};
+export type NotifMeta = VideoHiddenMeta | VideoWatchedMeta;
 
 export interface Notification {
   id: number;