app: fix leaderboard auto-refresh via @gr .render(key=...)

In Gradio 6.14 a `gr.Dataframe` identity-checks its component id and
short-circuits the diff when the new value's shape + column structure
look unchanged, even when the row data differs. That swallowed
updates from `every=` on the Dataframe AND from
`gr.Timer().tick(outputs=df_view)` AND from a manual Refresh button
click: the server-side fetch ran every tick (`Loaded 10 rows from
Hub` in logs) but the browser never saw the new rows. Only a full
page reload picked them up.

Documented fix (post Gradio's March 2026 Dataframe overhaul): wrap
the component in `@gr.render` and give the inner Dataframe a `key=`
that changes on every tick. Gradio then tears down and rebuilds the
component subtree in place, picking up the fresh value instead of
trying to diff in place.

Shape:
- tick_state: gr.State holding a ms-timestamp that bumps on every
refresh; included in the Dataframe `key=`.
- table_state: gr.State holding the pandas DataFrame.
- `_refresh_table()` runs once per tick, returns
(new_df, new_tick); writes both via outputs=[table_state,
tick_state]. One server-side fetch shared across all subscribers
per tick instead of N viewers x N fetches.
- `@gr.render(inputs=[table_state, tick_state])` rebuilds the
Dataframe with `key=f"leaderboard-df-{t}"` each tick.
- gr.Timer(10).tick wires _refresh_table; Refresh button click
wires the same function.

Verified locally against the live submissions dataset: 10 rows render
correctly (including the latest `Auto-refresh test BETA` row);
server-side Timer ticks every 10s (`Loaded 10 rows from Hub` lines
in the local log).

Diagnosis credit: Leandro reviewed the symptoms and pointed at the
Gradio 6 identity-diff failure mode + the @gr .render(key=) workaround;
this is his pattern.

app.py

@@ -6,6 +6,7 @@ Read path lives in :mod:`leaderboard`. Submit-tab validation lives in
 from __future__ import annotations
 
 import logging
+import time
 
 import gradio as gr
 
@@ -49,20 +50,43 @@ with gr.Blocks(title="CADGenBench Leaderboard") as app:
     )
 
     with gr.Tab("Leaderboard"):
-        df_view = gr.Dataframe(
-            value=load_leaderboard,
-            interactive=False,
-            wrap=True,
-            label="Results (sorted by aggregate CAD score)",
-        )
-        # gr.Dataframe's built-in `every=` doesn't reliably re-render
-        # when rows are added between ticks (gradio-app/gradio#8160).
-        # Drive periodic updates through an explicit gr.Timer event,
-        # same code path as the manual Refresh button.
+        # Gradio 6's gr.Dataframe identity-checks its component id and
+        # short-circuits the diff when the new value's shape + column
+        # structure look unchanged, even though the row data differs.
+        # That swallows updates from every= on the Dataframe AND from
+        # gr.Timer().tick(outputs=df_view) AND from a manual refresh
+        # button click. The fix is @gr.render with a `key=` that
+        # changes on every tick: Gradio tears down and rebuilds the
+        # component subtree in place, picking up the fresh value.
+        #
+        # The fetch happens once per tick in `_refresh_table` (server
+        # side) and the result rides on gr.State to all subscribers,
+        # so N concurrent viewers don't cause N HTTPS GETs per tick.
+        table_state = gr.State(value=load_leaderboard())
+        tick_state = gr.State(value=0)
+
+        @gr.render(inputs=[table_state, tick_state])
+        def render_leaderboard(df, t: int) -> None:
+            gr.Dataframe(
+                value=df,
+                interactive=False,
+                wrap=True,
+                label="Results (sorted by aggregate CAD score)",
+                key=f"leaderboard-df-{t}",
+            )
+
+        def _refresh_table():
+            # ms-resolution so rapid clicks always increment the key.
+            return load_leaderboard(), int(time.time() * 1000)
+
         auto_refresh_timer = gr.Timer(10)
-        auto_refresh_timer.tick(fn=load_leaderboard, outputs=df_view)
+        auto_refresh_timer.tick(
+            fn=_refresh_table, outputs=[table_state, tick_state],
+        )
         refresh_btn = gr.Button("Refresh", size="sm")
-        refresh_btn.click(fn=load_leaderboard, outputs=df_view)
+        refresh_btn.click(
+            fn=_refresh_table, outputs=[table_state, tick_state],
+        )
 
     with gr.Tab("Submit"):
         gr.Markdown(