Executables model has drifted from the core script's pretext.cfg: no jing entry, three vestigial keys #1200

The v2 Executables model (pretext/project/xml.py) and the core script's pretext/pretext.cfg have drifted apart in both directions.

Missing: jing. The core script gained a jing executable key on 2026-07-04, used for local schema validation with a consolidated report. The model has no such field, and since it is declared extra="forbid", a jing attribute in a project's executables.ptx is a hard parse error rather than being ignored. Is there a reason we cannot have a jing entry? Without one, a user with jing outside the search path has no way to point the CLI at it.

Vestigial: liblouis, pdfsvg, pdfpng. None of these executables has been invoked by the core script for some time:

• liblouis (default file2brl): unused since May 2023, when the current braille pipeline became the only one; braille text translation now goes through the louis Python bindings. The key was removed from pretext.cfg in Script: remove the obsolete "liblouis" executable key pretext#3099.
• pdfsvg (default pdf2svg): removed from pretext.cfg 2024-06-30, in favor of the pyMuPDF library.
• pdfpng (default convert): removed from pretext.cfg 2025-01-03, likewise pyMuPDF.

Related: the LegacyExecutables model requires a <liblouis> element, so legacy-format project.ptx manifests cannot drop the entry until that field is relaxed; the example manifests in the core repository keep it for exactly that reason.

For reference, the core script's current executables set: latex, pdflatex, xelatex, asy, mermaid (mmdc), sage, pdfeps (pdftops), node, perl, fop, jing.

Claude Fable 5, acting as a coding assistant for Rob Beezer