ui: ProblemCard/ConcludeCard redesigned — the solution is the hero

Owner round (2026-10-05), Slice C:

- ProblemCard: ALWAYS OPEN — the answered card's container + eyebrow
  discipline ('Problem' label, lh-prose statement), no chevron, no
  collapsed bar. The dock mirrors it in Slice D.
- ConcludeCard: the reveal is the modelSolution committed at POSE time,
  shown verbatim as the hero — never re-authored (the slim schema's
  law). The verdict rides below in the quiz-explanation register
  (small, muted 'Verdict:' row). Nothing collapsible. Legacy inputs
  with their own solutionReveal fall back to it.
- The reveal join: modelSolutionForConclude (native-messages.ts) — the
  newest cleanly-posed problem before the conclude call; refused poses
  reveal nothing. projectView enriches tool-conclude parts with
  part.reveal at projection; ArtifactPartProps carries the field
  (contracts/chat.ts).

Pinned: always-open problem card; hero-first conclude layout with the
verdict after it; legacy fallback; the join (clean pose, refused pose,
multi-problem records) and the view enrichment.

src/core/contracts/chat.ts

@@ -270,5 +270,9 @@ export interface ArtifactPartProps {
 		toolCallId: string;
 		input?: unknown;
 		output?: unknown;
+		/** The view-seam join for conclude cards (owner round, 2026-10-05):
+		 *  the modelSolution committed at POSE time, folded onto the part by
+		 *  projectView — the reveal is never re-authored. */
+		reveal?: unknown;
 	};
 }

src/core/native-messages.ts

@@ -328,6 +328,40 @@ function cleanToolCallIds(messages: readonly LhMessage[]): Set<string> {
 	return ids;
 }
 
+/** The conclusion's reveal (owner round, 2026-10-05): the hero of a
+ *  conclude card is the modelSolution committed at POSE time — the newest
+ *  cleanly-posed problem BEFORE this conclude call. The reveal is never
+ *  re-authored (the slim schema dropped solutionReveal); legacy conclude
+ *  inputs that still carry their own solutionReveal fall back to it at the
+ *  card. Undefined when the pose carries no string solution. */
+export function modelSolutionForConclude(
+	messages: readonly LhMessage[],
+	concludeCallId: string,
+): string | undefined {
+	let mi = messages.findIndex(
+		(m) =>
+			(m as { role?: string }).role === "assistant" &&
+			(m as AssistantMessage).content.some(
+				(b) => b.type === "toolCall" && b.id === concludeCallId,
+			),
+	);
+	if (mi < 0) return undefined;
+	const clean = cleanToolCallIds(messages);
+	for (; mi >= 0; mi--) {
+		const m = messages[mi]!;
+		if ((m as { role?: string }).role !== "assistant") continue;
+		const assistant = m as AssistantMessage;
+		for (let bi = assistant.content.length - 1; bi >= 0; bi--) {
+			const block = assistant.content[bi]!;
+			if (block.type !== "toolCall" || block.name !== PRACTICE_PROBLEM_TOOL) continue;
+			if (!clean.has(block.id)) continue; // a refused pose revealed nothing
+			const solution = (block.arguments as { modelSolution?: unknown } | undefined)?.modelSolution;
+			return typeof solution === "string" ? solution : undefined;
+		}
+	}
+	return undefined;
+}
+
 export function activeProblemOf(
 	messages: readonly LhMessage[],
 ): { toolCallId: string; input: unknown } | null {

src/core/view.ts

@@ -34,6 +34,7 @@
 
 import type { AssistantMessage, ToolResultMessage } from "@earendil-works/pi-ai";
 import type { LhMarkerMessage, LhMessage } from "./native-messages.ts";
+import { modelSolutionForConclude, PRACTICE_CONCLUDE_TOOL } from "./native-messages.ts";
 import { QUESTION_TOOLS } from "./pending.ts";
 import type { SubagentArtifactData, SubagentResultMeta } from "./contracts/jobs.ts";
 import type { PlanBlockData } from "./contracts/chat.ts";
@@ -194,7 +195,14 @@ export function projectView(messages: readonly LhMessage[], live?: LiveTurnState
 				} else if (block.type === "thinking") {
 					reasoning.push({ type: "reasoning", id: `${m.id}-r${reasoningN++}`, text: block.thinking, state: "done" });
 				} else if (block.type === "toolCall") {
-					rest.push(toolPartOf(block, live, streamingMessage));
+					const part = toolPartOf(block, live, streamingMessage);
+					// The conclusion's reveal join (owner round, 2026-10-05): the
+					// hero of a conclude card is the modelSolution committed at POSE
+					// time — a record fold, enriched here so the card renders pure.
+					if (block.name === PRACTICE_CONCLUDE_TOOL) {
+						part.reveal = modelSolutionForConclude(messages, block.id);
+					}
+					rest.push(part);
 				}
 			}
 			const parts: LhViewPart[] = [...reasoning, ...rest];