Decide how the CC BY-SA licence footer survives the cutover: a theme default or a per-repo footer.md #203

Part of #147 (parity study 2026-09-11 — decisions).

Problem

Every lecture page built with quantecon-book-theme ends with the same footer: a CC BY-SA 4.0 badge, the sentence "Creative Commons License – This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International." and "A theme by QuantEcon". The footer is written straight into the page template with no condition around it, so every Sphinx lecture site shows it without configuring anything (layout.html L353-L361).

This theme renders a footer only when a site sets site.parts.footer (PageContent.tsx L105). The part is declared with no default in template.yml L20-L22, and SiteFooter.tsx L6-L22 renders whatever Markdown the site supplies. With the part unset, the page has no footer at all: no licence notice and no theme credit. Nothing under app/ reads MyST's license field. docs/layout.md L39-L48 says the part matches "the Sphinx sites' footer block", but it gives no standard content and no warning that leaving the part out removes the licence notice. Neither docs/ nor README.md mentions a licence.

The content-driven footer was a deliberate choice. PLAN.md L59 lists "content-driven footer" as already at parity, and the comparison table in #33 recorded the footer as "Parity (improved: configurable)". Neither says that the licence notice is no longer shown by default.

Where the consumers stand:

#147 records the cutover as all-or-nothing, with every lecture series moving at once. Any series that moves without its own footer.md loses the licence notice, as lecture-wasm already has.

Decision needed

When a site sets no site.parts.footer, should the theme supply the licence notice and theme credit itself, or should adding footer.md be a documented migration step for each lecture repo?

Points that bear on the options:

• Where option 1 gets its text. The default could be hard-coded, as the Sphinx theme does, or built from MyST's project.license. That field does reach the theme: the fork lists license among the project frontmatter keys (project/types.ts L16-L21) and copies project frontmatter into the site manifest (manifest.ts L143-L167). But neither lecture-wasm's myst.yml nor the jb2 one sets it, so building from it would trade a footer.md for a license: entry in each repo. The per-repo step would remain.
• Option 2 cannot be enforced through template.yml. Marking the part required would not catch a missing footer. The site build validates the template's options and frontmatter but not its parts (manifest.ts L370-L385), and validateParts runs only inside MystTemplate.prepare (template.ts L201-L218), which the site build does not call.
• The theme credit. Whether "A theme by QuantEcon" stays is part of this decision. Under option 1 the theme decides. Under option 2 each repo's footer.md does.

Report's lean: the study recommends adding this to the #147 gate as a decision to settle before the cutover. It names both options and does not choose between them.

Acceptance criteria

• The decision is recorded on this issue: option 1 (saying whether the default is hard-coded or built from project.license) or option 2.
• The decision says whether "A theme by QuantEcon" stays, and where it is set.
• If option 1: a site without site.parts.footer renders the licence notice (and the credit, if kept), a site with the part renders only its own content, and a test covers the unset case.
• If option 2: docs/layout.md shows the standard footer.md content and warns that leaving the part unset removes the licence notice. footer.md is also listed as a per-repo step in the cutover migration plan (Lecture repos moving off the Sphinx theme have no checklist of what myst.yml and CI must now set #209), or in PLAN.md's "Consumer migration" checklist until that plan exists.
• PLAN.md:59 is no longer edited: PLAN.md gets a closing note instead of row edits (Close out PLAN.md now that the parity plan is complete #218).
• An issue or PR in QuantEcon/lecture-wasm is linked here to restore the notice on that site, either through a footer.md or through a theme bump that carries the default.

Context

• Source: the 2026-09-11 book-theme parity study, row F015. The recheck moved it from implemented to partial, with medium confidence because the content-driven design is recorded as intended. Section 3.1 of the report recommends adding it to the Book-theme parity cutover — tracking #147 gate as a decision. Section 3.4 lists footer.md for the migration checklist (Lecture repos moving off the Sphinx theme have no checklist of what myst.yml and CI must now set #209) and PLAN.md:58-59 for correction (PLAN.md and the user docs claim book-theme parity and behaviour that the code does not deliver #210).
• Verified 2026-09-11: the live lecture-wasm site shows no licence or Creative Commons text.
• Related: Light-mode site footer falls short of WCAG AA once the 70% opacity is composited #201 (light-mode footer contrast at 70% opacity) is a separate issue. It concerns how the footer is drawn, not whether it appears, so it applies under either option.
• Earlier comparison: see Technical Review & Feature Comparison — February 2026 #33, the February 2026 comparison that recorded the footer as parity.
• Out of scope (the two themes do not differ here):
  • "Powered by" names MyST Markdown here (Outline.tsx L135-L137), where the Sphinx theme names Jupyter Book (layout.html L239).
  • Neither theme shows previous/next links. The Sphinx prev_next macro (layout.html L245-L254) is never called. In this theme, the loader returns the getFooterLinks result (loaders.server.ts L102-L105) but nothing renders it.