Writer does not emit `\'` for apostrophes that the reader would otherwise reject as quote opens

[rundel]

The reader rejects a bare ' between a letter and a space as an unmatched smart-quote open (Q-2-10) and instructs the user to escape it as \'. The reader correctly accepts the escaped form and produces an apostrophe in the AST. The writer, however, drops the escape: given a Pandoc AST containing the apostrophe, it emits ' rather than \', so its output fails to re-parse through the reader.

$ printf -- "reveal.js\\' jump-to-slide.\n" | cargo run --bin pampa -- 2>&1
[ Para [Str "reveal.js’", Space, Str "jump-to-slide."] ]

$ printf -- "reveal.js\\' jump-to-slide.\n" | cargo run --bin pampa -- -t qmd 2>&1
reveal.js' jump-to-slide.

$ printf -- "reveal.js\\' jump-to-slide.\n" | cargo run --bin pampa -- -t qmd 2>/dev/null | cargo run --bin pampa -- 2>&1
Error: [Q-2-10] Closed Quote Without Matching Open Quote
   ╭─[ <stdin>:1:11 ]
   │
 1 │ reveal.js' jump-to-slide.
   │          ┬┬
   │          ╰─── This is the opening quote. If you need an apostrophe, escape it with a backslash.
   │           │
   │           ╰── A space is causing a quote mark to be interpreted as a quotation close.
───╯

The writer needs to escape ' back to \' whenever the surrounding context (letter on the left, whitespace on the right) would cause the reader to misclassify it as a quote open.

In the wild (quarto-web):

• https://github.com/quarto-dev/quarto-web/blob/baeab38627fcc3f3a9ea3ca3ea689ece413df65d/docs/presentations/revealjs/presenting.qmd#L85
• https://github.com/quarto-dev/quarto-web/blob/baeab38627fcc3f3a9ea3ca3ea689ece413df65d/docs/authoring/tables.qmd#L772