gallery: stop negative-caching render fetches

Renders land after boot (a submission completes, or an existing row is
backfilled), so lru_cache was pinning boot-time 404s and keeping
thumbnails dashed until the next restart. Drop the memoization on the
render byte-fetchers; hf_hub_download keeps its own per-revision disk
cache, so re-fetching an unchanged thumbnail stays cheap. Also picks up
the 3 baseline rows' just-backfilled renders on this redeploy.

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

app.py

@@ -523,14 +523,15 @@ def serve_report(submission_id: str) -> Response:
 GALLERY_THUMB_VIEW = "iso"
 
 
-@lru_cache(maxsize=512)
 def _fetch_render(submission_id: str, fixture: str) -> bytes | None:
     """Pull a submission's gallery thumbnail (``renders/<id>/<fixture>.png``).
 
-    Cached in-process so repeated scrolls past the same thumbnail don't
-    re-hit the Hub. Returns ``None`` on any failure so the caller serves
-    a clean 404 (the gallery only requests this for fixtures it already
-    knows are valid, so a miss here is genuinely unexpected/transient).
+    Deliberately **not** memoized: renders land over time (a submission
+    completes, or an existing row is backfilled) after the Space process
+    booted, so negative-caching a boot-time miss would keep a thumbnail
+    dashed until the next restart. ``hf_hub_download`` does its own disk
+    caching per revision, so a re-fetch of an unchanged file stays cheap.
+    Returns ``None`` on any failure (the gallery draws the dashed cell).
     """
     try:
         local_path = hf_hub_download(
@@ -547,7 +548,6 @@ def _fetch_render(submission_id: str, fixture: str) -> bytes | None:
         return None
 
 
-@lru_cache(maxsize=256)
 def _fetch_gt_render(fixture: str) -> bytes | None:
     """Pull a fixture's ground-truth thumbnail from the private GT dataset.
 
@@ -555,7 +555,10 @@ def _fetch_gt_render(fixture: str) -> bytes | None:
     ``cadgenbench.common.paths.data_gt_dir``). GT renders are a property
     of the data revision, not of any submission, so they're served
     straight from the GT repo rather than duplicated per submission.
-    Needs the Space ``HF_TOKEN``'s read scope on the private repo.
+    Not memoized for the same reason as :func:`_fetch_render` (GT
+    renders can be added/updated on a data revision bump);
+    ``hf_hub_download`` handles the per-revision disk cache. Needs the
+    Space ``HF_TOKEN``'s read scope on the private repo.
     """
     try:
         local_path = hf_hub_download(