practice: ONE send lane — the register is read from the text

Owner round 2 (2026-10-05), Slice H: the Nudge/Commit two-lane buttons
are gone. One Send; Enter sends, Shift+Enter is a newline. Whether a
submission claims an answer is apparent from the thinking itself — the
agent reads it (hint ladder for traces, moves+verdict for claims).

- The thinking input loses the commit field end-to-end: ChatInput,
  parseChatInput, newThinkingMessage (details and the model-facing label
  both collapse to the single 'Your thinking'), the optimistic marker.
- Legacy records' commit flags are deliberately unread.
- Doctrine: the two labeled channels become one read instruction; 'answer
  commits' section retitled 'Claimed answers' — a claim is not a
  progress signal.
- ThinkingCard: one label, collapsed arrival (the unified row).
- The dock placeholder no longer explains lanes that no longer exist.

components/chat.tsx

@@ -448,16 +448,16 @@ export function Chat({
 		void resumeStream();
 	}, [resumeStream]);
 
-	// The practice dock's two lanes (owner, 2026-10-04): both POST one
-	// thinking input against the ACTIVE problem — commit=false is the
-	// nudge (hint request), commit=true the answer commit. Each starts a
-	// turn; the dock stays mounted (the problem is still active until the
-	// agent concludes).
+	// The practice dock's send (ONE lane, owner 2026-10-05): POSTs the
+	// thinking against the ACTIVE problem — whether it claims an answer is
+	// read from the text by the agent, not declared here. Starts a turn;
+	// the dock stays mounted (the problem is still active until the agent
+	// concludes).
 	const submitThinking = useCallback(
-		(commit: boolean, text: string) => {
+		(text: string) => {
 			const problem = activeProblemRef.current;
 			if (!problem) return;
-			void send({ type: "thinking", problemCallId: problem.toolCallId, commit, text });
+			void send({ type: "thinking", problemCallId: problem.toolCallId, text });
 		},
 		[send],
 	);
@@ -1631,7 +1631,7 @@ function DockOverlay({
 	 *  question (the composer is replaced); null in teaching sessions. */
 	practice: { toolCallId: string; input: unknown } | null;
 	/** (commit, text) — the practice dock's two submit lanes. */
-	onSubmitThinking: (commit: boolean, text: string) => void;
+	onSubmitThinking: (text: string) => void;
 	/** Teach-phase pending question: arrives collapsed behind the reveal button (W5). */
 	requiresReveal: boolean;
 	/** The reading-thinking draft (owner 2026-10-03) — owned by ChatView so