Mobile browsers report readyState === OPEN after background suspension
even though the OS killed the TCP connection. The per-pane visibility
handlers skipped reconnection in that case, leaving the pane frozen
until TCP keepalive fired (30–120 s on cellular).
Remove the readyState guard and unconditionally replace the socket on
visibility return — same pattern the events socket already uses. Also
let pageshow/online fire recovery without the visibilityState gate,
since some mobile browsers fire pageshow before updating that property.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
