feat: add video duration to YouTube announcements

Fetches duration via InnerTube player API for new videos at
announcement time. Displayed as compact h:mm:ss before views/likes.
Gracefully omitted for Shorts and unavailable content.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/youtube.py

@@ -137,6 +137,47 @@ def _resolve_via_innertube(video_id: str) -> str | None:
     return None
 
 
+def _fetch_duration(video_id: str) -> int:
+    """Fetch video duration in seconds via InnerTube player API. Blocking.
+
+    Returns 0 on failure or for live content.
+    """
+    payload = json.dumps({
+        "context": {
+            "client": {
+                "clientName": "WEB",
+                "clientVersion": _YT_CLIENT_VERSION,
+            },
+        },
+        "videoId": video_id,
+    }).encode()
+    req = urllib.request.Request(_YT_PLAYER_URL, data=payload, method="POST")
+    req.add_header("Content-Type", "application/json")
+    try:
+        resp = _urlopen(req, timeout=_FETCH_TIMEOUT)
+        raw = resp.read()
+        resp.close()
+        data = json.loads(raw)
+        details = data.get("videoDetails") or {}
+        if details.get("isLiveContent") and details.get("isLive"):
+            return 0
+        secs = int(details.get("lengthSeconds", 0))
+        return secs
+    except Exception:
+        return 0
+
+
+def _format_duration(seconds: int) -> str:
+    """Format seconds as compact duration: 62 -> '1:02', 3661 -> '1:01:01'."""
+    if seconds <= 0:
+        return ""
+    h, rem = divmod(seconds, 3600)
+    m, s = divmod(rem, 60)
+    if h:
+        return f"{h}:{m:02d}:{s:02d}"
+    return f"{m}:{s:02d}"
+
+
 def _resolve_channel(url: str) -> str | None:
     """Fetch YouTube page HTML and extract channel ID. Blocking.
 
@@ -337,11 +378,32 @@ async def _poll_once(bot, key: str, announce: bool = True) -> None:
         channel = data["channel"]
         name = data["name"]
         shown = new_items[:_MAX_ANNOUNCE]
+        # Fetch durations for announced videos concurrently
+        durations: dict[str, int] = {}
+        video_ids = []
+        for item in shown:
+            vid = item["id"].removeprefix("yt:video:")
+            if vid != item["id"]:
+                video_ids.append((item["id"], vid))
+        if video_ids:
+            futs = {
+                item_id: loop.run_in_executor(None, _fetch_duration, vid)
+                for item_id, vid in video_ids
+            }
+            for item_id, fut in futs.items():
+                try:
+                    durations[item_id] = await fut
+                except Exception:
+                    pass
         for item in shown:
             title = _truncate(item["title"]) if item["title"] else "(no title)"
             link = item["link"]
             # Build metadata suffix
             parts = []
+            dur = durations.get(item["id"], 0)
+            dur_str = _format_duration(dur)
+            if dur_str:
+                parts.append(dur_str)
             views = item.get("views", 0)
             likes = item.get("likes", 0)
             if views: