extras: notebooks that are not sections (#53)

[project-delphi]

Closes #53.

The repo had no concept of a notebook outside the twelve sections, and two places actively refused one: check_links.py failed any .ipynb it could not match to a declared section, and gen_notebooks.py built every header and footer out of sections.sNN. The two deep dives that follow are take-home material rather than sections, so the kind has to exist before either can be committed.

extras: in _variables.yml

A new top-level mapping: sections: minus minutes, start, end and part. That absence is the mechanism — scripts/timeline.py only ever walks sections, so nothing declared under extras: can move a start time, the agenda or workshop.minutes. Extras get no #sec-NN slide anchor and no Kahoot.

Two are declared: 12 · Matrix factorizations and 13 · Tensor factorizations.

The changes

• scripts/gen_notebooks.py — iterates SECTIONS + EXTRAS. The format line drops part and minutes when they are absent; the footer gives an extra no Kahoot block, chains Next up within the extras, and closes the last one on a link back to the site rather than on the workshop's closing words. Section 11 still does not point at extra 12: the workshop ends there.
• scripts/check_links.py — extras are notebooks in checks 1 (validity, badges), 3 (Colab URLs) and 8 (solution independence), and are absent from checks 4 (deck anchors), 5 (landing-page parity) and 6 (the clock). Check 6 needed no change by construction, which is the point.
• scripts/gen_tables.py — three new generated tables: _includes/notebooks-extra-en.md for notebooks.qmd, and _includes/extras-en.md / extras-es.md for the README's two language halves. Columns are # | Deep dive | Colab — no Slides column, because an extra has no deck anchor, and no Quiz column, because no Kahoot covers one.
• README.md — a ## Going further / ## Para seguir heading in each language half, wrapping new marker regions injected by the existing inject() helper. The 165/195-minute prose is untouched: it is about the timed day, not about what is in notebooks/.
• notebooks.qmd — a ## Going further section, two new rows in the hand-written What each notebook needs table, and the subtitle reworded off the bare word "Twelve".
• notebooks/README.md, CLAUDE.md — the same rewording, plus a short section on what an extra is and which checks it does and does not belong to.
• notebooks/12-*.ipynb, notebooks/13-*.ipynb — placeholder notebooks with their generated header and footer and a scope table. The teaching bodies arrive in the two follow-up issues.

Acceptance

• gen_tables.py and gen_notebooks.py are byte-stable on a second run — verified, zero files changed.
• check_links.py passes all nine checks with the two extras declared:
  • [1] 14 notebooks (12 sections, 2 extras): valid, no outputs, no execution counts, badges self-consistent
  • [3] 64 Colab URLs, all well-formed, 14/14 notebooks referenced
  • [4] 15 anchors present in both decks, no extras in either
  • [5] both pages list all 12 sections with slide anchors and notebook links
  • [6] 12 sections end at +03:15 — 195 min including quizzes and breaks
  • [8] 145 visible code cells across 14 notebooks are self-sufficient
• The generated agenda includes are byte-identical to main.
• quarto render (1.6.40) run and docs/ committed. That render also picks up the twelve section notebooks in docs/notebooks/, which were stale from the previous merge.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Bis2w9X1oAX9MEVvKh4Ndo

[project-delphi]

close #53