Reflow joins two source lines and the join changes how the rest of the block is read

Tier 1 (formatting corrupts output). Measured at 14e23234.

Reflow joins two source lines that Asciidoctor keeps apart, and the join changes how the LINES AFTER IT are read. Two faces.

Face 1 — the item's principal text

input:  "* a\nX\n// c\n+\npara\n** b\n"
output: "* a X\n// c\n+\npara\n** b\n"

render(input):  <li><p>a X</p><div class="paragraph"><p>para ** b</p></div></li>
render(output): <li><p>a X</p><div class="paragraph"><p>para</p></div>
                <div class="ulist"><ul><li><p>b</p></li></ul></div></li>

Every byte from // c onward is identical in both. Only the principal text's line break is gone — and with it Asciidoctor's reading of the +-attached block: ** b folds into the attached paragraph before the join and starts a nested list after it. Dropping either ingredient makes it render-equal ("* a\nX\n+\npara\n** b\n" without the comment line, "* a\n// c\n+\npara\n** b\n" without the join), so both are load-bearing.

Face 2 — a block title, and the block under it

input:  "* a\n[role]\npara\n[[anc]]\n.T\npara\n"
output: "* a\n[role]\npara\n[[anc]]\n.T para\n"

render(input):  …<div id="anc" class="paragraph"><div class="title">T</div><p>para</p></div>
render(output): the item has no attached block at all

The .T block-title line is reflowed onto the paragraph it titles. .T para is then a title with nothing under it, and the whole anchored paragraph — title AND text — disappears from the rendering. This face LOSES CONTENT rather than reshaping it.

5 of the 158 shapes on the deep sweep's allowlist fail for this reason (4 of face 1, 1 of face 2). Pinned by the deep sweep's allowlist (tests/format/list-shape-allowlist.ts, family reflow-join-changes-reading); run it with bun run sweep:deep.

Start with tests/format/list-shape-allowlist.ts and the reflow-join-changes-reading family, then run the listed allowlist with bun run sweep:deep. Compare the five failing shapes against the input and rendered-output examples; done means those shapes no longer change how later lines are read or lose the anchored block.