diff --git a/components/answered-card.tsx b/components/answered-card.tsx
index abf5aa4..b989cee 100644
--- a/components/answered-card.tsx
+++ b/components/answered-card.tsx
@@ -101,7 +101,7 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 			)}
 
 			{answer.text && <div className="lh-prose mt-2 whitespace-pre-wrap">“{answer.text}”</div>}
-			{answer.dontKnow && (isQuiz || isExplain) && (
+			{answer.dontKnow && isQuiz && (
 				<div className="mt-2 text-sm text-muted-foreground">Answered “I don't know”.</div>
 			)}
 
@@ -126,23 +126,12 @@ export function AnsweredCard({ answer }: { answer: QuestionAnswerData }) {
 				</div>
 			)}
 			{/* The explain reveal (owner ruling 2026-09-27): the committed answer
-			    and its explanation, shown on submit — no verdict, the model's next
-			    reply IS the grading. */}
-			{isExplain && (answer.committed || answer.explanation) && (
+			    — one field, reasoning included — shown on submit; no verdict,
+			    the model's next reply IS the grading. */}
+			{isExplain && answer.committed && (
 				<div className="mt-3 rounded-lg bg-muted py-2 text-sm text-muted-foreground">
-					{answer.committed && (
-						<>
-							<span className="font-medium text-foreground">The answer: </span>
-							<MessageResponse className="inline [&_p]:inline [&_p]:m-0">{answer.committed}</MessageResponse>
-						</>
-					)}
-					{answer.committed && answer.explanation && <div className="my-1" />}
-					{answer.explanation && (
-						<>
-							<span className="font-medium text-foreground">Why: </span>
-							<MessageResponse className="inline [&_p]:inline [&_p]:m-0">{answer.explanation}</MessageResponse>
-						</>
-					)}
+					<span className="font-medium text-foreground">The answer: </span>
+					<MessageResponse className="inline [&_p]:inline [&_p]:m-0">{answer.committed}</MessageResponse>
 				</div>
 			)}
 		</div>
diff --git a/components/question-dock.tsx b/components/question-dock.tsx
index f42eb82..213a9fd 100644
--- a/components/question-dock.tsx
+++ b/components/question-dock.tsx
@@ -248,8 +248,9 @@ function QuestionDockForm({
 		if (explainInput) {
 			// The commitment rides the question data (never sent to the
 			// client before answering) and snapshots into the answer at submit.
+			// One field, reasoning included — no separate explanation
+			// (owner ruling 2026-09-27).
 			q.committedAnswer = explainInput.correctAnswer;
-			q.explanation = explainInput.explanation;
 		}
 		return q;
 	}, [toolCallId, kind, input]);
@@ -285,7 +286,7 @@ function QuestionDockForm({
 
 	const canSubmit =
 		qd.mode === "text"
-			? sel.dontKnow || text.trim().length > 0 // explain: dontKnow is a first-class answer
+			? text.trim().length > 0
 			: sel.dontKnow || (sel.otherSelected && other.trim().length > 0) || sel.selected.size > 0;
 
 	const submit = () => {
@@ -324,14 +325,14 @@ function QuestionDockForm({
 	const otherInputRef = useRef<HTMLInputElement>(null);
 	const thinkingRef = useRef<HTMLTextAreaElement>(null);
 	// One row past the options is the trailing row: quiz → don't-know,
-	// ask → Other (a question never has both). Explain has exactly ONE
-	// row — its don't-know (there are no options to walk).
+	// ask → Other (a question never has both). Text mode (ask/explain)
+	// has no rows — the composer IS the answer surface.
 	const optionCount = qd.mode === "text" ? 0 : qd.options.length;
-	const rowCount = qd.mode === "text" ? (kind === "explain" ? 1 : 0) : optionCount + 1;
+	const rowCount = qd.mode === "text" ? 0 : optionCount + 1;
 
 	const kbdAct = (idx: number) => {
 		if (idx < optionCount) toggle(idx);
-		else if (kind === "quiz" || kind === "explain")
+		else if (kind === "quiz")
 			setSel((prev) => ({ ...prev, selected: new Set(), otherSelected: false, dontKnow: !prev.dontKnow }));
 		else {
 			// Space on the ask's Other row (owner refinement round,
@@ -435,10 +436,7 @@ function QuestionDockForm({
 					</div>
 				)}
 
-				{/* Text-mode questions render no options list — EXCEPT explain,
-				    whose single "I don't know" row is the one walkable answer
-				    (kbd row 0). The answer itself goes in the composer below. */}
-				{(qd.mode !== "text" || kind === "explain") && (
+				{qd.mode !== "text" && (
 					<div className="flex flex-col gap-2 pb-2" role={qd.mode === "multi-select" ? "group" : "radiogroup"}>
 						{qd.options.map((opt, i) => {
 							const isSel = sel.selected.has(i);
@@ -484,7 +482,7 @@ function QuestionDockForm({
 							);
 						})}
 
-						{(kind === "quiz" || kind === "explain") && (
+						{kind === "quiz" && (
 							<button
 								type="button"
 								onClick={() =>
diff --git a/src/agent/prompts/shared/20-question-tools.md b/src/agent/prompts/shared/20-question-tools.md
index c6b379b..d6609ea 100644
--- a/src/agent/prompts/shared/20-question-tools.md
+++ b/src/agent/prompts/shared/20-question-tools.md
@@ -4,9 +4,8 @@ Two instruments. The quiz tool (its exact name depends on the quizzing mechanic
 
 ### Quiz checks — shared doctrine
 
-- `explanation` (required) says why the correct answer is correct. It comes BEFORE `correctAnswer` in the call by design: reason it out first, then commit to the answer the reasoning supports.
-- An "I don't know" choice is always available to the learner — never author your own opt-out. A dontKnow result is a genuine gap, not a wrong answer.
-- Answers may carry a free-text `note` — read it; it says what he was thinking.
+- Multiple choice carries a separate `explanation` (why the correct option is correct, written BEFORE `correctAnswer`: reason it out first, then commit). Free recall has ONE field — `correctAnswer`, the committed answer with its reasoning inside.
+- Option-style answers may carry a free-text `note` — read it; it says what he was thinking.
 - ONE question per turn: ask, then end your turn — his answer determines the next.
 
 ### `ask_user_question`
diff --git a/src/agent/tools.ts b/src/agent/tools.ts
index 92c7d24..6cf55fd 100644
--- a/src/agent/tools.ts
+++ b/src/agent/tools.ts
@@ -113,12 +113,11 @@ const QUIZ_OPTION_CRAFT =
  *  the teach variant appends the nodeId tagging paragraph. */
 const EXPLAIN_DOCTRINE =
 	"Ask the learner to EXPLAIN something in his own words — a graded check with NO options: he types a free-text " +
-	"answer. Unlike ask_user_question (no right answer), explain always has one. THE COMMITMENT RULE: write " +
-	"explanation (your reasoning) first, then correctAnswer — the FULL correct answer, committed before he ever sees " +
-	"the question. When his answer returns, grade it strictly against your committed answer in your reply: never " +
+	"answer. Unlike ask_user_question (no right answer), explain always has one. THE COMMITMENT RULE: write correctAnswer — the FULL " +
+	"correct answer in your own words, reasoning included — committed before he ever sees the question. When his answer returns, grade it strictly against your committed answer in your reply: never " +
 	"revise the commitment after seeing his words, and never mark a wrong answer right to be kind — a near-miss is " +
-	"partial understanding; name exactly what he got and what he missed. He sees the committed answer and the " +
-	"explanation on submit. An 'I don't know' choice is always available to him — a genuine gap, not a wrong answer. " +
+	"partial understanding; name exactly what he got and what he missed. He sees the committed answer on submit. If he genuinely doesn't know, he says so in his own words — that is a genuine " +
+	"gap, not a wrong answer. " +
 	"ONE question per turn: call a single explain, then end your turn — his answer determines the next.";
 
 export const probeQuizTool: AgentTool<typeof probeQuizInputSchema> = {
diff --git a/src/core/question-core.ts b/src/core/question-core.ts
index 99d8064..b78fcdf 100644
--- a/src/core/question-core.ts
+++ b/src/core/question-core.ts
@@ -224,26 +224,22 @@ export const probeQuizInputSchema = quizInputBase;
 // correct answer BEFORE posing (the commitment rides the persisted call
 // args, is revealed to the learner on submit, and is restated in the answer
 // result the model grades against; the client never grades free text).
-// Mechanics doctrine lives in the TOOL DESCRIPTIONS (owner ruling
-// 2026-09-27: pi-native — doctrine travels with the armed tool), not in
-// the system prompt.
+// ONE committed answer, reasoning included (owner ruling 2026-09-27: the
+// separate explanation field was quiz remnant — collapsed away).
+// Mechanics doctrine lives in the TOOL DESCRIPTIONS (pi-native ruling),
+// not in the system prompt.
 
 export const explainInputBase = Type.Object({
 	question: Type.String({
 		description:
 			"The single question to ask. ONE question per turn: ask, then end your turn — the answer determines the next.",
 	}),
-	explanation: Type.String({
-		description:
-			"REQUIRED. Explanation revealed AFTER the learner answers (shown however he did). It is written BEFORE " +
-			"correctAnswer by design: reason it out first, then commit to the answer the reasoning supports.",
-	}),
 	correctAnswer: Type.String({
 		description:
-			"REQUIRED. The full correct answer in your own words — COMMITTED before the learner ever sees the question. " +
-			"The commitment is immutable: when his answer returns, grade it strictly against this text — never revise the " +
-			"commitment after seeing his words, and never mark a wrong answer right to be kind. Both this and the explanation " +
-			"are shown to him on submit; your next reply grades the nuance of what he wrote.",
+			"REQUIRED. The full correct answer in your own words, reasoning included — COMMITTED before the learner " +
+			"ever sees the question. The commitment is immutable: when his answer returns, grade it strictly against this " +
+			"text — never revise the commitment after seeing his words, and never mark a wrong answer right to be kind. " +
+			"It is shown to him on submit; your next reply grades the nuance of what he wrote.",
 	}),
 	details: Type.Optional(
 		Type.String({ description: "Optional extra context or instructions shown under the question." }),
@@ -338,6 +334,7 @@ export interface QuestionData {
 	correctIndices?: number[];
 	// explain only. NEVER send to the client before answering:
 	committedAnswer?: string;
+	// quiz only (the MC "why"). NEVER send to the client before answering:
 	explanation?: string;
 	createdAt: string;
 }
@@ -356,7 +353,7 @@ export interface QuestionAnswerData {
 	correct?: boolean; // quiz only
 	correctIndices?: number[]; // quiz only (rendering)
 	committed?: string; // explain only (rendering): the model's committed answer
-	explanation?: string; // quiz/explain only (rendering)
+	explanation?: string; // quiz only (rendering)
 	dismissed?: boolean;
 	answeredAt: string;
 }
@@ -595,9 +592,8 @@ export function buildAnswer(qd: QuestionData, req: AnswerRequest): QuestionAnswe
 	}
 	if (qd.kind === "explain") {
 		// No client grading — the model grades in its reply, against the
-		// commitment. Snapshots ride along for the reveal + rendering.
+		// commitment. The commitment snapshots for the reveal + rendering.
 		base.committed = qd.committedAnswer;
-		base.explanation = qd.explanation;
 	}
 	return base;
 }
@@ -627,13 +623,9 @@ export function formatAnswerMessage(ad: QuestionAnswerData): string {
 		}
 		lines.push(`Correct: ${correctStr}`);
 	} else if (ad.kind === "explain") {
-		if (ad.dontKnow) {
-			lines.push(
-				`The learner selected "I don't know" — they did NOT attempt an answer (a genuine knowledge gap, not a wrong guess).`,
-			);
-		} else {
-			lines.push(`The learner answered: ${ad.text ?? "(no answer)"}`);
-		}
+		// No opt-out row on explain (owner ruling 2026-09-27): if he doesn't
+		// know, he says so in his own words — his text is all there is.
+		lines.push(`The learner answered: ${ad.text ?? "(no answer)"}`);
 		if (ad.committed) {
 			lines.push(`Your committed correct answer (immutable — grade against it, never revise it): ${ad.committed}`);
 		}
diff --git a/tests/chat-flow.test.ts b/tests/chat-flow.test.ts
index 55507a1..0618e61 100644
--- a/tests/chat-flow.test.ts
+++ b/tests/chat-flow.test.ts
@@ -1057,8 +1057,7 @@ describe("background-turn runner (owner ruling 2026-09-25: every turn is a serve
 it("explain tool call persists as a pending part; the free-text answer reveals the commitment and reaches the model", async () => {
 	const EXPLAIN_INPUT = {
 		question: "Explain why Mercury is hard to observe.",
-		explanation: "It never strays far from the Sun in our sky.",
-		correctAnswer: "Its small angular separation from the Sun.",
+		correctAnswer: "Its small angular separation from the Sun — it never strays far from the Sun in our sky.",
 		nodeId: "planet-order",
 	};
 	const { engine, calls } = scriptedTeacher((cs) => [
@@ -1108,7 +1107,6 @@ it("explain tool call persists as a pending part; the free-text answer reveals t
 		mode: "text",
 		options: [],
 		committedAnswer: EXPLAIN_INPUT.correctAnswer,
-		explanation: EXPLAIN_INPUT.explanation,
 		createdAt: new Date().toISOString(),
 	};
 	const answer = buildAnswer(qd, { text: "It stays near the Sun." });
@@ -1122,7 +1120,7 @@ it("explain tool call persists as a pending part; the free-text answer reveals t
 	assert.equal((part as { state?: string }).state, "output-available");
 	const out = (part as { output?: { committed?: string; explanation?: string } }).output!;
 	assert.equal(out.committed, EXPLAIN_INPUT.correctAnswer, "the commitment snapshots into the answer record");
-	assert.equal(out.explanation, EXPLAIN_INPUT.explanation);
+	assert.equal(out.explanation, undefined, "no explanation remnant — one committed field (owner 2026-09-27)");
 
 	// The model's continuation saw the answer JSON (fork 1: the answer IS
 	// the call's tool result) — his text AND the commitment snapshot ride it.
@@ -1130,5 +1128,6 @@ it("explain tool call persists as a pending part; the free-text answer reveals t
 	assert.match(seen, /It stays near the Sun\./);
 	assert.match(seen, /committed/);
 	assert.match(seen, /small angular separation/);
+	assert.ok(!/"explanation"/.test(seen), "the answer record carries no explanation field");
 	assert.equal(danglingQuestionOf(saved2.messages), null, "no pending question remains");
 });
diff --git a/tests/question-core.test.ts b/tests/question-core.test.ts
index 037a74a..0efe705 100644
--- a/tests/question-core.test.ts
+++ b/tests/question-core.test.ts
@@ -550,11 +550,11 @@ describe("dock selection (toggleOption / toggleOther)", () => {
 // ─── the explain tool: free-recall quizzing (owner 2026-09-27) ─────────────
 
 describe("explainInputBase / explainInputProblems (the commitment contract)", () => {
-	it("commits the argument order: explanation (reasoning) BEFORE correctAnswer (the pick)", () => {
-		// Same ruling as the quiz (2026-09-25): models emit tool args in
-		// schema order — reasoning first, then the answer it supports.
+	it("has ONE authoring field — no explanation remnant (owner ruling 2026-09-27)", () => {
+		// The MC quiz's explanation/answer split was quiz baggage: free
+		// recall commits a single correctAnswer, reasoning included.
 		const keys = Object.keys(explainInputBase.properties);
-		assert.ok(keys.indexOf("explanation") < keys.indexOf("correctAnswer"));
+		assert.deepEqual(keys, ["question", "correctAnswer", "details"]);
 	});
 
 	it("the teach object adds the required nodeId AFTER the base fields", () => {
@@ -577,8 +577,7 @@ describe("buildAnswer / formatAnswerMessage: explain", () => {
 		question: "Why does the Michelson-Morley null result matter?",
 		mode: "text",
 		options: [],
-		committedAnswer: "It ruled out the luminiferous aether and set up special relativity.",
-		explanation: "A stationary aether would produce a fringe shift; none was observed.",
+		committedAnswer: "It ruled out the luminiferous aether — a stationary aether would produce a fringe shift, none was observed — and set up special relativity.",
 		createdAt: new Date().toISOString(),
 		...overrides,
 	});
@@ -587,7 +586,7 @@ describe("buildAnswer / formatAnswerMessage: explain", () => {
 		const ad = buildAnswer(explainQD(), { text: "Something about light speed being constant?" });
 		assert.equal(ad.correct, undefined, "no client verdict — the model grades in its reply");
 		assert.equal(ad.correctIndices, undefined);
-		assert.equal(ad.committed, "It ruled out the luminiferous aether and set up special relativity.");
+		assert.equal(ad.committed, "It ruled out the luminiferous aether — a stationary aether would produce a fringe shift, none was observed — and set up special relativity.");
 		assert.equal(ad.text, "Something about light speed being constant?");
 	});
 
@@ -608,9 +607,4 @@ describe("buildAnswer / formatAnswerMessage: explain", () => {
 		assert.match(text, /Grade his answer strictly/);
 	});
 
-	it("formats dontKnow as a gap, not a guess", () => {
-		const text = formatAnswerMessage(buildAnswer(explainQD(), { dontKnow: true }));
-		assert.match(text, /did NOT attempt/);
-		assert.ok(!text.includes("The learner answered:"), "no phantom answer beside the gap");
-	});
 });
diff --git a/tests/question-tools.test.ts b/tests/question-tools.test.ts
index 35c0c90..1208a0b 100644
--- a/tests/question-tools.test.ts
+++ b/tests/question-tools.test.ts
@@ -317,8 +317,7 @@ describe("prepareQuestionArguments (the string-encoded options wobble)", () => {
 describe("teachExplainToolFor: the explain variant validates nodeId like the quiz", () => {
 	const validExplain = {
 		question: "Explain why the null result matters.",
-		explanation: "A stationary aether predicts a fringe shift.",
-		correctAnswer: "It ruled out the aether.",
+		correctAnswer: "It ruled out the aether — a stationary aether predicts a fringe shift, and none was seen.",
 		nodeId: "arith",
 	};
 
@@ -374,13 +373,11 @@ describe("the prober's explain: no nodeId field at all", () => {
 		assert.ok(!("nodeId" in probeExplainTool.parameters.properties));
 		const res = await boundaryParse(probeExplainTool, {
 			question: "Explain what a derivative measures.",
-			explanation: "It is instantaneous rate of change.",
-			correctAnswer: "The instantaneous rate of change.",
+			correctAnswer: "The instantaneous rate of change at a point — the limit the slopes converge to.",
 		});
 		assert.equal(res.success, true);
 		const empty = await boundaryParse(probeExplainTool, {
 			question: "q",
-			explanation: "e",
 			correctAnswer: " ",
 		});
 		assert.equal(empty.success, false);
diff --git a/tests/render-cards.test.tsx b/tests/render-cards.test.tsx
index 143fb72..751a66b 100644
--- a/tests/render-cards.test.tsx
+++ b/tests/render-cards.test.tsx
@@ -467,18 +467,18 @@ describe("AnsweredCard: the explain variant", () => {
 		question: "Explain why the null result matters.",
 		mode: "text",
 		options: [],
-		committedAnswer: "It ruled out the luminiferous aether.",
-		explanation: "A stationary aether predicts a fringe shift; none was seen.",
+		committedAnswer: "It ruled out the luminiferous aether — a stationary aether predicts a fringe shift, and none was seen.",
 		createdAt: new Date().toISOString(),
 	});
 
-	it("reveals the committed answer + explanation with NO verdict chips", () => {
+	it("reveals the single committed answer (reasoning inside it) with NO verdict chips", () => {
 		const html = renderToStaticMarkup(<AnsweredCard answer={buildAnswer(explainQD(), { text: "Something about relativity?" })} />);
 		assert.match(html, /Explain/, "labeled as the explain kind");
 		assert.match(html, /The answer:/);
 		assert.match(html, /luminiferous aether/);
-		assert.match(html, /Why:/);
-		assert.ok(!html.includes("incorrect") && !html.includes("correct</") , "no client grading");
+		assert.match(html, /fringe shift/);
+		assert.ok(!html.includes("Why:"), "no separate explanation field — one committed answer (owner 2026-09-27)");
+		assert.ok(!html.includes("incorrect") && !html.includes("correct</"), "no client grading");
 		assert.ok(!html.includes('data-mark="x"') && !html.includes('data-mark="check"'));
 	});
 
@@ -487,9 +487,4 @@ describe("AnsweredCard: the explain variant", () => {
 		assert.match(html, /Something about relativity\?/);
 	});
 
-	it("dontKnow renders as the gap, not a wrong answer", () => {
-		const html = renderToStaticMarkup(<AnsweredCard answer={buildAnswer(explainQD(), { dontKnow: true })} />);
-		assert.match(html, /I don&#x27;t know/);
-		assert.ok(!html.includes("The learner answered:"));
-	});
 });
diff --git a/tests/tool-parts.test.ts b/tests/tool-parts.test.ts
index eecd2f8..cf216d2 100644
--- a/tests/tool-parts.test.ts
+++ b/tests/tool-parts.test.ts
@@ -273,8 +273,7 @@ describe("display-math newline rule (Option A, owner ruling 2026-09-27)", () =>
 describe("parseExplainInput: the dock's display seam for explain calls", () => {
 	const good = {
 		question: "Explain why Mercury is hard to observe.",
-		explanation: "It never strays far from the Sun in our sky.",
-		correctAnswer: "Its small angular separation from the Sun.",
+		correctAnswer: "Its small angular separation from the Sun — it never strays far from the Sun in our sky.",
 		nodeId: "planet-order", // the teacher's field — STRIPPED by Clean, like quiz
 		details: "Think about where it appears at dusk.",
 	};
@@ -282,7 +281,7 @@ describe("parseExplainInput: the dock's display seam for explain calls", () => {
 	it("parses a valid call and strips the teacher-only nodeId", () => {
 		const parsed = parseExplainInput(good)!;
 		assert.equal(parsed.question, "Explain why Mercury is hard to observe.");
-		assert.equal(parsed.correctAnswer, "Its small angular separation from the Sun.");
+		assert.equal(parsed.correctAnswer, "Its small angular separation from the Sun — it never strays far from the Sun in our sky.");
 		assert.equal(parsed.details, "Think about where it appears at dusk.");
 		assert.ok(!("nodeId" in parsed), "the teacher-only key is cleaned away");
 	});