Replace the manual "Disconnected → Reconnect button" screen with a small
top-banner that retries the WS up to 8 times (500ms → 5s, ~27s budget).
On open, snapshot replay restores the question card and countdown so a
brief network blip is invisible to the student. After the retry budget
exhausts, fall back to a manual "Reload" card.
Same path covers initial WS-open failures (transient TLS hiccups on the
Aliyun edge), since the first connect() and subsequent reconnects share
the schedule. Auth-related closes (1008) still hard-reload immediately
so an invalidated cookie lands on the join form, not in a retry loop.
Submits are now also gated on ws.readyState === OPEN; clicks during a
reconnect are silent no-ops, and the question re-renders fresh once the
server replays state.
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