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/contracts/chat.ts

@@ -186,8 +186,10 @@ export const HANDOFF_TEXT =
 /** The model-facing register of a thinking submission (newThinkingMessage
  *  prefixes the learner's text with this label). Hints and commits ride
  *  one channel — the label is the ONLY difference the model sees. */
-export const THINKING_HINT_LABEL = "Thinking trace (working, not committed)";
-export const THINKING_COMMIT_LABEL = "Committed answer";
+/** The single submission label (owner round, 2026-10-05): one send
+ *  lane — whether a submission claims an answer is read from the text,
+ *  not declared by a button. */
+export const THINKING_LABEL = "Your thinking";
 
 /** The conclude tool's ack — shared by the executed call (agent layer) and
  *  the dismissal-synthesized pair (input-events), so a concluded problem