docs/API.md gains the endpoint and what it returns, why `play` is the bigger
and lesser of the two, the element-by-id route found while probing, and the
per-library shapes with the traps in them — the string "true", the inline cloze
markers, the correct-option-first convention, and the UI subtrees that drown an
exercise in button labels.
CLAUDE.md's "no quiz of its own" note said a contentId was the only handle onto
the content. That was the reason nobody looked further, so it now says where to
look instead.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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