fix: board dropdown accepts a stale value instead of killing the Gradio queue

app.py

@@ -23,6 +23,12 @@ ArrayExpress) and ``citation`` is never rendered at all.
 Failures are surfaced by who owns them: a bad file tells the submitter exactly
 what to fix; an evaluator-side failure says "our side, please retry" and logs
 the traceback rather than blaming the submission.
+
+The board dropdown takes ``allow_custom_value``: its choices are only filled once
+the registry loads, so a browser holding a value from an earlier version of the
+page -- or any load where the registry is briefly unreachable -- would otherwise
+be refused by Gradio's own preprocessing, before ``by_slug`` gets the chance to
+fall back to the hero board.
 """
 
 import os
@@ -410,6 +416,7 @@ def build_demo() -> gr.Blocks:
                 board_sel = gr.Dropdown(
                     label="Board",
                     choices=[],
+                    allow_custom_value=True,
                     info="A slice of the benchmark: one modality, area or task family.",
                 )
                 board_head = gr.HTML()