feat: .md download bundles thumbnails, auto-cache on channel add

- Bulk 'Download .md' now also caches thumbnails (one action does both);
  removed the redundant standalone Thumbnails button from the bulk action bar.
- Scrape UX optimization: batch job skips videos whose .md already exists
  (just caches their thumbnail) instead of re-extracting.
- Auto-thumbnails: on addChannel, thumbnails cache in the background so a
  newly-attached channel's catalog looks populated immediately, even before
  any .md is generated.
- Thumbnail fallback: pending videos without a stored thumbnail URL use the
  canonical https://i.ytimg.com/vi/<id>/hqdefault.jpg, so every video shows
  a thumbnail (and /api/thumbnails/{id} never 404s — redirects if uncached).
- New helpers in pipeline.py: thumbnail_url_for() + cache_thumbnail().

src/yt_scraper/pipeline.py

@@ -140,6 +140,32 @@ def _safe_dirname(name: str) -> str:
     return safe.strip().strip(".") or "unknown"
 
 
+def thumbnail_url_for(video_row) -> str:
+    """Thumbnail URL for a video: stored URL, else the canonical YouTube one derived from its id."""
+    if video_row and getattr(video_row, "thumbnail", None):
+        return video_row.thumbnail
+    vid = getattr(video_row, "video_id", "") if video_row else ""
+    return f"https://i.ytimg.com/vi/{vid}/hqdefault.jpg"
+
+
+def cache_thumbnail(store, video_id: str, thumbnails_dir) -> bool:
+    """Download + cache a video's thumbnail to <thumbnails_dir>/<video_id>.jpg. Returns True on success/existing."""
+    import requests as _requests
+    out = Path(thumbnails_dir) / f"{video_id}.jpg"
+    if out.exists():
+        return True
+    v = store.get_video(video_id)
+    url = thumbnail_url_for(v) if v else f"https://i.ytimg.com/vi/{video_id}/hqdefault.jpg"
+    try:
+        r = _requests.get(url, timeout=15, headers={"User-Agent": "Mozilla/5.0"})
+        r.raise_for_status()
+        out.parent.mkdir(parents=True, exist_ok=True)
+        out.write_bytes(r.content)
+        return True
+    except Exception:
+        return False
+
+
 def re_render_videos(store: Store, cfg: Config, channel_id: str | None = None) -> int:
     """Regenerate .md for done videos that have stored segments. Returns count re-rendered."""
     import json

src/yt_scraper/webapp/api.py

@@ -332,41 +332,29 @@ def build_router(store: Store, cfg: Config, jobs) -> APIRouter:
     # -------------------------------------------------- thumbnails (local cache)
     @r.post("/tools/thumbnails")
     async def download_thumbnails(payload: dict):
-        import requests as _req
+        from ..pipeline import cache_thumbnail
         video_ids = (payload or {}).get("video_ids") or []
         channel_id = (payload or {}).get("channel_id")
         if channel_id and not video_ids:
-            video_ids = [v.video_id for v in store.get_all(channel_id) if v.thumbnail]
+            video_ids = [v.video_id for v in store.get_all(channel_id)]
         out_dir = Path(cfg.output_dir_resolved).parent / "thumbnails"
         out_dir.mkdir(parents=True, exist_ok=True)
         n = 0
         for vid in video_ids:
-            v = store.get_video(vid)
-            if not v or not v.thumbnail:
-                continue
-            target = out_dir / f"{vid}.jpg"
-            if target.exists():
+            if cache_thumbnail(store, vid, out_dir):
                 n += 1
-                continue
-            try:
-                r2 = _req.get(v.thumbnail, timeout=15, headers={"User-Agent": "Mozilla/5.0"})
-                r2.raise_for_status()
-                target.write_bytes(r2.content)
-                n += 1
-            except Exception:
-                continue
         return {"downloaded": n, "dir": str(out_dir)}
 
     @r.get("/thumbnails/{video_id}")
     def serve_thumbnail(video_id: str):
         from fastapi.responses import RedirectResponse
+        from ..pipeline import thumbnail_url_for
         local = Path(cfg.output_dir_resolved).parent / "thumbnails" / f"{video_id}.jpg"
         if local.exists():
             return FileResponse(str(local), media_type="image/jpeg")
         v = store.get_video(video_id)
-        if v and v.thumbnail:
-            return RedirectResponse(url=v.thumbnail, status_code=302)
-        raise HTTPException(404, "no thumbnail")
+        url = thumbnail_url_for(v) if v else f"https://i.ytimg.com/vi/{video_id}/hqdefault.jpg"
+        return RedirectResponse(url=url, status_code=302)
 
     # -------------------------------------------------- clip (transcript segment)
     @r.get("/clip/{video_id}")

src/yt_scraper/webapp/jobs.py

@@ -108,12 +108,14 @@ class JobManager:
         return (name, row.channel_id, url)
 
     def _run_batch(self, job_id: str, opts: dict[str, Any]) -> None:
+        from ..pipeline import process_video as _process_video, cache_thumbnail
         video_ids = opts.get("video_ids") or []
         cookie_path = opts.get("cookies_file") or resolve_active_path(self.store)
+        thumb_dir = Path(self.cfg.output_dir_resolved).parent / "thumbnails"
         total = len(video_ids)
         self.store.update_job(job_id, status="running", total=total, completed=0)
         self._emit(job_id, "progress", {"completed": 0, "total": total})
-        self._emit(job_id, "log", {"msg": f"processing {total} videos"})
+        self._emit(job_id, "log", {"msg": f"processing {total} videos (.md + thumbnails)"})
         cfg = _clone_config(self.cfg)
         if opts.get("languages"):
             cfg.languages = opts["languages"]
@@ -129,12 +131,20 @@ class JobManager:
                 completed += 1
                 self.store.update_job(job_id, completed=completed)
                 continue
+            # UX optimization: skip re-extracting videos whose .md already exists — just ensure thumbnail cached.
+            md_path = Path(cfg.output_dir_resolved).parent / row.markdown_path if row.markdown_path else None
+            if row.status == "done" and row.markdown_path and md_path and md_path.exists():
+                cache_thumbnail(self.store, vid, thumb_dir)
+                status = "done"
+                self._emit(job_id, "log", {"msg": f"cached {vid} (md already present)"})
+            else:
                 channel_name, channel_id, channel_url = self._resolve_channel_for_video(vid)
-            status = process_video(
+                status = _process_video(
                     row, cfg, self.store, channel_name, channel_id, channel_url,
                     cookies_file=cookie_path,
                     on_log=lambda m: self._emit(job_id, "log", {"msg": m}),
                 )
+                cache_thumbnail(self.store, vid, thumb_dir)
             completed += 1
             self.store.update_job(job_id, completed=completed)
             self._emit(job_id, "progress", {"completed": completed, "total": total, "video_id": vid, "status": status})

src/yt_scraper/webapp/static/app.js

@@ -184,6 +184,12 @@
           this.forms.channelUrl = "";
           await this.loadChannels();
           this.toast("Added " + (d.name || "channel") + " (" + (d.video_count || 0) + " videos)");
+          // Auto-cache thumbnails in the background so the catalog looks populated immediately
+          if (d.channel_id) {
+            this.api("/api/tools/thumbnails", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ channel_id: d.channel_id }) })
+              .then((r) => { if (r && r.downloaded) this.toast((r.downloaded) + " thumbnails cached"); })
+              .catch(() => {});
+          }
         } catch (e) { this.forms.channelError = e.message; }
         finally { this.loading.addChannel = false; }
       },
@@ -302,7 +308,7 @@
         if (!ids.length) { this.toast("No videos selected", "error"); return; }
         try {
           const d = await this.api("/api/scrape/batch", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ video_ids: ids }) });
-          this.toast("Batch .md job started: " + (d.count || ids.length) + " videos");
+          this.toast("Downloading .md + thumbnails for " + (d.count || ids.length) + " videos");
           this.subscribeJob(d.job_id, "batch");
           if (!videoIds) this.selectNone();
         } catch (e) { this.toast("Batch failed: " + e.message, "error"); }

src/yt_scraper/webapp/static/index.html

@@ -213,13 +213,9 @@
           <template x-if="videos.selected.length > 0">
             <div class="bulk-bar glass p-3 flex flex-wrap items-center gap-2">
               <span class="pill accent-grad btn-primary font-bold" x-text="videos.selected.length + ' selected'"></span>
-              <button class="btn accent-grad btn-primary !py-1.5 !px-3 text-xs" @click="downloadMdBatch()">
+              <button class="btn accent-grad btn-primary !py-1.5 !px-3 text-xs" @click="downloadMdBatch()" title="Download .md + thumbnails for the selection">
                 <svg class="w-3.5 h-3.5" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path stroke-linecap="round" stroke-linejoin="round" d="M12 4v12m0 0l-4-4m4 4l4-4M4 18v2h16v-2"/></svg>
-                Download .md
-              </button>
-              <button class="btn btn-ghost !py-1.5 !px-3 text-xs" @click="downloadThumbnails()">
-                <svg class="w-3.5 h-3.5" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path stroke-linecap="round" stroke-linejoin="round" d="M3 16.5v2.25A2.25 2.25 0 005.25 21h13.5A2.25 2.25 0 0021 18.75V16.5M16.5 12L12 7.5 7.5 12M12 7.5V18"/></svg>
-                Thumbnails
+                Download .md + thumbs
               </button>
               <button class="btn btn-ghost !py-1.5 !px-3 text-xs" @click="downloadAudio()">
                 <svg class="w-3.5 h-3.5" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path stroke-linecap="round" stroke-linejoin="round" d="M9 18V6l10-2v12M9 18a3 3 0 11-6 0 3 3 0 016 0zm10-2a3 3 0 11-6 0 3 3 0 016 0z"/></svg>