A marker item's + with two blanks inside a directive pair prints one blank and the next block attaches

What happens

A marker item whose tail + is followed by two blank lines, inside a preprocessor conditional pair, is printed with one blank line, and the block below attaches to the item:

:x:
ifdef::x[]
* a
+


next para
endif::[]

formats to :x:\nifdef::x[]\n* a\n+\n\nnext para\nendif::[]\n (the + survives, the blank run narrows). The input renders next para outside the list; the output pulls it into the item. Verified at main 3e7ace33: render changes, output is a fixed point, so the corruption is silent and stable. Ruby 2.0.26 and the JS port agree on both readings.

Mechanism

The bare-marker twin of #269: an armed tail whose pop is withheld, where the two-blank run is the only carrier of detachment. Outside a directive pair the printer's separator rule handles this (the #171/#259 landings); the Sep 7 review measured the state reachable only via insideDirectivePair (3 of 1,646 documents searched, 0 in the reference corpus). Found by the review's reader-feasibility seat; its findings file (plus-reader-findings.md, finding F6) has the trace.

Whether the #269 fix candidate (ItemBody.droppedLiveTail, prototyped Sep 7, plus-prototype-findings.md) reaches this state was not measured; its grids carried no directive pairs. The lane that lands the #269 fix should add this witness to its grid and report which fact arm, if any, carries it.

Related

#269, #274, #325 (row R4's family), #202/#248 (family arms).

Start with plus-reader-findings.md, finding F6, and compare the witness with the #269 fix candidate described in plus-prototype-findings.md. Add this directive-pair case to the candidate's grid and trace whether any fact arm preserves the two-blank separator. Done means reporting whether the candidate reaches this state and which fact arm, if any, carries it.