/* everything above went out in this one turn. A call that waits on
           the one before it can only have issued its first here, so this is
           the number that says the boot chain is still going out in one
           round — 10 before this round, 23 after it — and the walk holds a
           floor against it. */
        boot.sync = boot.calls;
        /* two frames: the first is the shell, the second is the first one
           the app could have drawn anything into. A phone producing no
           frames at all (launched straight into the background) seals on
           the timer instead, well before the walk's first probe — the
           census must never depend on something that might not happen. */
        const sealTimer = setTimeout(sealBoot, 1200);
        requestAnimationFrame(() => requestAnimationFrame(() => { clearTimeout(sealTimer); sealBoot(); }));