Speed up large movement gallery entry (Byzantine)

Hall frames use thumbs only (never multi-MB originals). Preload no longer blocks open; texture downloads are queued; boot overlay no longer waits on HDR Environment.

Co-authored-by: Cursor <cursoragent@cursor.com>

Documentation/basics.md

@@ -210,7 +210,7 @@ Pan, zoom, and era/event click-to-zoom only update **local** `viewStart` / `view
 | Overlay **“Loading art history…”** | Until the first catalog fetch (`bounds` + `timeline` + `artists`) completes |
 | Bottom banner **“Loading portraits…”** | While artist portrait thumbnails are still downloading on the movement flow (timeline stays interactive) |
 | Overlay **“Opening artist/movement gallery…”** / **“Loading artists…”** | Between clicking a portrait/movement and the 3D hall (or artist-filter modal) data being ready |
-| Overlay **“Loading gallery…”** | While the 3D canvas initializes, HDR Environment settles, or door/hall shaders warm up after the hall opens (painting images continue loading after the overlay dismisses) |
+| Overlay **“Loading gallery…”** | While the 3D canvas initializes and door/hall shaders warm up after the hall opens (HDR Environment and painting textures continue in the background) |
 | Overlay **“Loading paintings…”** | Brief counter while wall painting textures start downloading; large halls (e.g. Byzantine) keep loading after the overlay dismisses — a slow image no longer permanently blanks the frame |
 | Overlay **“Restoring gallery…”** | Briefly after WebGL context loss while the canvas remounts |
 
@@ -373,9 +373,9 @@ Full guide: [tours.md](tours.md).
 
 ### Shared 3D behaviour
 
-**3D images** prefer local thumbnail files (`galleryImageUrlCandidates` in `client/src/api/client.ts`: thumb → full → `GET /api/paintings/:id/image?size=thumb`). Remote Wikipedia fetches are too slow for realtime WebGL textures; the client calls `POST /api/artists/:id/preload-images` or `POST /api/movements/:id/preload-images` automatically when entering an **artist** or **movement** hall (public routes — link disk files and regenerate missing thumbs). While a texture is loading, the frame shows the canvas cover instead of a white placeholder. A per-image deadline only releases the boot overlay counter — it does **not** permanently blank the frame if the download finishes later (important for large halls such as Byzantine).
+**3D images** prefer local **thumbnail** files (`galleryImageUrlCandidates` in `client/src/api/client.ts`: thumb → `GET /api/paintings/:id/image?size=thumb`; full originals are **not** used for hall frames — they can be tens of MB and made large halls take ~1 minute). Remote Wikipedia fetches are too slow for realtime WebGL textures. Entering an **artist** or **movement** hall fires `POST /api/artists/:id/preload-images` or `POST /api/movements/:id/preload-images` in the **background** (does not block hall open). Texture downloads are **queued** (max 8 parallel). While a texture is loading, the frame shows the canvas cover instead of a white placeholder. A per-image deadline only releases the boot overlay counter — it does **not** permanently blank the frame if the download finishes later.
 
-**Boot overlay** (`VirtualGallery.tsx`): the center shows **“Loading gallery…”** until the WebGL canvas is ready, HDR `Environment` has settled (or timed out / failed), and a one-shot `gl.compileAsync` warm-up finishes so entrance doors / passages (often frustum-culled at spawn) do not hitch on the first turn. Painting textures keep loading in the background (prefer thumbnails; fallback to full / on-demand API; GPU upload after decode) so large halls (50+ works) are not stuck on the overlay. Env and shader warm-up also have short timeouts. The 3D hall stays mounted while painting detail or bio overlays are open; returning remounts the canvas when the hall becomes active again.
+**Boot overlay** (`VirtualGallery.tsx`): the center shows **“Loading gallery…”** until the WebGL canvas is ready and a short `gl.compileAsync` warm-up finishes (so entrance doors / passages do not hitch on the first turn). HDR `Environment` loads in a Suspense boundary **without** blocking the overlay. Painting textures keep loading in the background. The 3D hall stays mounted while painting detail or bio overlays are open; returning remounts the canvas when the hall becomes active again.
 
 **WebGL context-loss recovery:** on some GPUs/drivers (notably certain Chrome setups) the browser can drop the WebGL context right after entering a hall, which would otherwise leave a permanent dark window. `VirtualGallery.tsx` listens for `webglcontextlost` / `webglcontextrestored`, calls `preventDefault()` so the browser can restore the context, and remounts the `<Canvas>` with a fresh context (a **“Restoring gallery…”** overlay shows briefly). The network-loaded HDR `Environment` map is wrapped in an error boundary so, if it fails to load, the hall still renders without reflections instead of unmounting the whole scene.
 
@@ -431,7 +431,7 @@ Next to the toggle, **Show more** (checkbox, persisted in `localStorage`) opens
 - **Guided tours** add curator-ordered winged halls with stop text on painting detail — [tours.md](tours.md).
 - **Wall hang** is shared: first work on the left at the entrance, last on the right.
 - **Influence-based hall links** connect artists through documented painting relationships, grouped by movement at the exit.
-- **3D gallery images** use locally cached files only; slow remote fetches would break realtime rendering. The client calls `POST /api/artists/:id/preload-images` or `POST /api/movements/:id/preload-images` automatically when entering an artist or movement hall (public routes — link disk files and regenerate missing thumbs).
+- **3D gallery images** use local **thumbnails** for hall frames (not multi-MB originals). `POST /api/artists/:id/preload-images` / `POST /api/movements/:id/preload-images` run in the background when entering a hall (public routes — link disk files and regenerate missing thumbs).
 - **3D gallery session** stays mounted while painting detail or bio overlays are open; returning to the hall remounts the WebGL canvas when it becomes active again.
 - **3D gallery resilience:** a lost WebGL context is recovered by remounting the canvas with a fresh context (rather than showing a dark window), and the HDR environment map is isolated behind an error boundary so its failure never blanks the scene.
 - **Loading feedback:** `GalleryLoadingMarker` surfaces catalog load, portrait download, gallery entry, painting-texture / GPU warm-up, Environment settle, and context-restore states so the user always knows work is still in progress.