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.

src/core/native-messages.ts

@@ -39,8 +39,7 @@ import { QUESTION_TOOLS } from "./pending.ts";
 import {
 	CONCLUDE_ACK_TEXT,
 	HANDOFF_TEXT,
-	THINKING_COMMIT_LABEL,
-	THINKING_HINT_LABEL,
+	THINKING_LABEL,
 } from "./contracts/chat.ts";
 import { compactAnswerForModel, type QuestionAnswerData } from "./question-core.ts";
 
@@ -224,20 +223,20 @@ export function newGraphContextMessage(picks: readonly GraphContextPick[], chain
 	};
 }
 
-/** The learner's thinking submission (the practice dock's two buttons):
- *  a user-register message the model reads WITH its label (hint vs
- *  commit — the register is the whole difference), while `details` keeps
- *  the raw payload for the transcript card. One problem may carry many
+/** The learner's thinking submission (ONE send lane, owner round
+ *  2026-10-05): the register is no longer declared by a button — the
+ *  model READS the text to tell working traces from claimed answers. The
+ *  content label is the single "Your thinking"; `details` keeps the raw
+ *  payload for the transcript card. One problem may carry many
  *  submissions. */
-export function newThinkingMessage(problemCallId: string, commit: boolean, text: string): LhMarkerMessage {
-	const label = commit ? THINKING_COMMIT_LABEL : THINKING_HINT_LABEL;
+export function newThinkingMessage(problemCallId: string, text: string): LhMarkerMessage {
 	return {
 		id: newMessageId(),
 		role: "custom",
 		customType: "practice-thinking",
-		content: `${label}:\n${text}`,
+		content: `${THINKING_LABEL}:\n${text}`,
 		display: true,
-		details: { problemCallId, commit, text },
+		details: { problemCallId, text },
 		timestamp: Date.now(),
 	};
 }