_getButtonCount re-implemented every button-visibility condition from build() and had already drifted: the screen-lock button incremented the built index but was never counted, so with rotation lock and screen lock both visible the reported total was one short and arrowRight on the last button silently died. Navigation now bounds against the actual built list, so there is no condition table left to drift; the dead onLoadSeekTimes sheet-compat callback invocation goes with it.
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