Two follow-up rulings on the explain tool:
1. No 'I don't know' row — not needed in free recall. If he doesn't
know, he says so in his own words; his text is the only answer
channel. Dock: text mode is rowless again (the composer IS the
surface); doctrine and the shared prompt chunk updated; the format
branch and card revert to quiz-only dontKnow.
2. explanation + correctAnswer collapse into ONE field — the separate
explanation was quiz remnant (MC needs the why outside its options;
a free-text commitment carries its own reasoning). Schema is now
{question, correctAnswer, details?}; the reveal shows the single
committed answer; no explanation snapshots anywhere on the explain
path.
1047/1047 tests, typecheck/lint/build green.