quiz answers carry a confidence slider — raw probability, snapped 0/30/50/70/90/100

Owner design round 2026-10-01: every multiple-choice quiz answer now
carries the learner's stated probability that his selected answer is
correct — calibration data for the prober and teacher, the flow itself
unchanged.

Definition (owner ruling, after weighing chance-normalization): RAW
probability. Sub-chance reports are diagnostic gold, not dead space —
'picked an option, believes it wrong' is a real state. The agents get
the sophistication: new shared/25-confidence.md composes for both
agents (chance level, sub-chance = distrusts the pick, correct+low =
fragile, wrong+high = committed misconception, IDK = genuine gap).

- question-core: AnswerRequest/QuestionAnswerData.confidence (quiz
  only, optional — old records valid), buildAnswer clamps and drops it
  on dontKnow, formatAnswerMessage states the line, CONFIDENCE_STOPS +
  DEFAULT_CONFIDENCE_INDEX exported.
- question-dock: snapped slider below 'I don't know', above 'Your
  thinking' — native range over the stop INDEX so ←/→ step the uneven
  grid cleanly, Tab chain rows → slider → thinking, Enter submits from
  the slider too. Rests at 50 and always sends (owner: 50 must mean a
  real coin flip, never 'untouched'). 'I don't know' GRAYS it out —
  layout holds, no value sent.

Deliberately untouched: explain free-recall card (quiz-only scope),
answered-card rendering of confidence, ask flow.

tests/prompt-overrides.test.ts

@@ -179,6 +179,7 @@ describe("the source-derived segment list", () => {
 				"system-prompt.md",
 				"prober/10-probe-doctrine.md",
 				"shared/20-question-tools.md",
+			"shared/25-confidence.md",
 				"shared/30-learner-files.md",
 				"shared/40-formatting.md",
 			],