trailingPlusPolicy recognises a refused passthrough from word count and glue instead of a recorded refusal

Split from #325, row R8 (verified at main ffdc1860).

The question: was this passthrough refused?

The reader's answer: nothing is recorded. scanPassthroughs (src/parse/inline/passthrough.ts) knows which candidates it refused and discards that.

The second answerer: src/print/text-edges.ts l.601, gluedToPredecessor = words.length === 1 && lead === "glue", which recognises "this + is the leftover of a passthrough the scan refused" from the shape of the surrounding words. The comment in passthrough.ts says the escape's correctness for \\+*b*+ DEPENDS on this arm.

Closes when: the reader records the refusal on the text node (a new recorded fact: fact-inventory row and parity family owed) and the printer reads it, with the word-shape test deleted; or a written reason the refusal is not a fact of the source (in which case the arm stays and this closes by decision). Red-first pin: a one-word glued text that is not a refused passthrough.

Related: #325 (the catalog), #90 (the class), #256 (escaped mark normal form).

Start in src/parse/inline/passthrough.ts and src/print/text-edges.ts, tracing the refused-candidate path and the gluedToPredecessor arm. Add the red-first coverage for a one-word glued text that is not a refused passthrough, then determine whether the refusal is recorded and consumed as a fact. Done means the word-shape test is deleted, or a written decision explains why the existing arm remains.