shouldHoldBootProgressForReauth (8d22781b1c, #95701) survived the rewrite
with no caller, so updateBootProgress let a running:true phase or a sibling
attempt's cleared error from an in-flight boot lift the recovery overlay and
re-arm the renderer's retry loop — the Sign in button flicker the helper
exists to stop. Gate updateBootProgress on it; re-emits of the latched
failure still pass so the non-retryable verdict is never lost.
db043ff445