Fix issue #1554: Preserve custom thumbnails in gallery script (#1649)

* Initial plan * Fix issue #1554: Preserve custom thumbnails in gallery script Modified scripts/generate_gallery.py to check if a thumbnail file already exists before extracting from notebooks. This prevents the script from overwriting manually-placed custom thumbnails in the _thumbnails directory. The gen_previews() method now: 1. Checks if self.png_path exists 2. If yes, logs info message and returns early (preserving custom thumbnail) 3. If no, proceeds with extraction from notebook or uses default logo Fixes #1554 --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Fix issue #1554: Preserve custom thumbnails in gallery script (#1649)
a99feb55 · Copilot · GitHub · db5178ba · a99feb55
--- a/scripts/generate_gallery.py
+++ b/scripts/generate_gallery.py
@@ -118,6 +118,13 @@ class NotebookGenerator:
        return None

    def gen_previews(self):
+        if self.png_path.exists():
+            logger.info(
+                f"Custom thumbnail already exists for {self.basename}, skipping extraction",
+                type="thumbnail_extractor",
+            )
+            return
+
        preview = self.extract_preview_pic()
        if preview is not None:
            with self.png_path.open("wb") as buff: