A plain-text output that keeps the object numbers, written as CommonMark
with GFM pipe tables, one .md per document-language in <lang>/markdown/,
(linked from the metadata page) with images into that shared directory
itself, skipping any already there, so --markdown alone still gives a complete tree.

provided as an alternative to --text rather than a replacement

--markdown  produces a document that renders, (both provide objext
  numbering survives both. Every object carries an anchor and a
  superscript number linking to itself, so a citation by object number
  is a link in any markdown renderer.
--text may still be of value to read in a terminal

A note is written where it is referenced, with a link back to the
object it came from, rather than gathered into an endnotes
section.

(assisted by Claude-Code)

typst provides a new pdf build path replacing latex as the primary pdf
builder.
  --typst (--typ) writes the .typ;
  --pdf writes the .typ and compiles it by spawning `typst compile`.
    (--pdf is redefined, being typst to pdf rather than latex).
  --latex is unchanged and writes the .tex;

One .typ per document-language (not one per paper size). The paper and
the orientation are read from sys.inputs with a default, so the same
file compiles to every paper --set-papersize asks for, the pdfs keep
their original names.

Spine's paper names (derived from what suited latex) and typst's are
different vocabularies and are mapped; a paper typst does not have is
named and skipped.

With the flag --pdf spine invokes a typesetter to generate the pdf
output directly, which is new (the latex path writes a .tex and leaves
xelatex to the caller). If typst is not available on the machine it is
reported absent, naming the binary and printing the command, and the run
continues, the .typ is written.

Several useful features of an object-centric pdf are easily met, usually
being a few lines each.
- The object number goes in the margin as one `place` at a coordinate
  inside the object's own block, carrying the label every citation
  points at.
- A note is a real footnote at the point of reference, with the
  document's own number and one link back to the object.
- The table of contents locates by object number rather than by page, so
  it holds true across every paper and every setting.

That typst compiles silently across the sample set means every internal
link in every document resolves (--pdf over the collection with two
paper sizes gives 144 pdfs, none skipped and none failed, each the page
size its name claims and each tagged).

paths: .typ, pdf named in same way as .tex based built pdfs so site
linkage works either way

flake.nix: added a typst dev shell, for .typ pdf typesetter
- dsh-typst-pdf providing a pdf typsetter for spine's .typ.
- dsh-latex-pdf provides xelatex for .tex which can still be written.

(assisted by Claude-Code)

Modules and imports rewritten to sisudoc.ocda.* and
sisudoc.outputs.*; dub.json excludedSourceFiles and the
spine:abstraction sub-package sourcePaths collapsed to
./src/sisudoc/ocda.

Verified: nix build .#spine-overlay-ldc clean.

(assisted by Claude-Code)

create new directories under ./src/sisudoc ocda & outputs in order to
separate the document abstraction library from downstream output
processing (stuff broken till paths & modules fixed)