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/session-core.ts

@@ -529,9 +529,9 @@ export class SessionModel {
 		if (input.type === "text") optimistic.push({ ...newUserMessage(input.text), id: localId() });
 		else if (input.type === "thinking") {
 			// The practice submissions (2026-10-04): the marker lands
-			// optimistically — the register (trace / commit) renders from
-			// its details the moment the button fires.
-			optimistic.push({ ...newThinkingMessage(input.problemCallId, input.commit, input.text), id: localId() });
+			// optimistically — the card renders from its details the
+			// moment the button fires.
+			optimistic.push({ ...newThinkingMessage(input.problemCallId, input.text), id: localId() });
 		} else if (input.type === "answer") {
 			const tool = pendingCallTool([...this.base, ...this.tail], input.toolCallId) ?? "quiz";
 			optimistic.push({ ...newAnswerResult(input.toolCallId, tool, input.answer), id: localId() });