fix: render long reference sidebars once instead of on every page

docs/user_guide/13-building.qmd

@@ -54,7 +54,8 @@ package metadata. See [Agent Skills](38-agent-skills.qmd) for details.
 package documentation. See [llms.txt](39-llms-txt.qmd) for details.
 
 11. Quarto renders all the source files into HTML, writing a companion Markdown (`.md`) file beside
-each page as it goes.
+each page as it goes. A long reference sidebar is rendered once and then copied into each of its
+pages, since building it again for every page takes much of the render time on a large API.
 
 After all steps complete, the finished site is in `docs/_site/`.
 

great_docs/_versioned_build.py

@@ -34,6 +34,7 @@
     version_url_segment,
 )
 from great_docs._website import page_metadata
+from great_docs._website.navigation import shared_sidebar
 
 if TYPE_CHECKING:
     from great_docs._api_diff import ApiSnapshot
@@ -2267,6 +2268,8 @@ def run_versioned_build(  # pragma: no cover
         _prune_missing_sidebar_pages(ver_dir)
         _rewrite_quarto_yml_for_version(ver_dir, entry, latest_tag)
         _sync_status_inline_script(ver_dir)
+        # Last, so the trimmed sidebars reflect every change above
+        shared_sidebar.prepare(ver_dir)
         pages_by_version[entry.tag] = pages
         dir_by_tag[entry.tag] = ver_dir