The Decoder's candidate 2 -- 'a focus/variant link means only one of the pair is
active' -- is answerable from the export and the answer is no.
It looked strong: ptloop01 carries opt_link=ptloop02.rat, it is the only linked
element on the title, the field comes straight from el.focus_link, and the port
never reads it.
But surveying opt_link across the whole export splits it in two: *f.rat targets
are variant-only, everything else is a top-level element drawn in its own right.
And the second population chains across kinds -- on main_menu, ptloop01 ->
ptloop02 -> ptbtn01 -> ptbtn01f. A light sweep points at a BUTTON, which a
variant selector cannot do.
So opt_link is a chain pointer that lands on the focus variant when the element
happens to be a button, which is why it was exported as focus_link. Candidate
eliminated; the port ignoring it is not what draws the extra sweep.
Surviving smaller finding: focus_link carries two different things and is named
after one. Nothing depends on it today.
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