fix(rectification): one stem on screen — a replaced focus draws nothing and the live one takes its slot (BUG-1135)

- GET attach: a live hanging focus replaces a superseded-unanswered focus
  linked to the last assistant turn instead of falling to a standalone copy.
- Client placement: a dead question on the latest message is replaceable,
  and the stem the body still ends with is stripped (stripQuestionSentences).
- Chat view: a dead question no longer turns the gap into 「没有拿到下一个问题」
  while the case has a different live question.
- Message entry: a superseded or replaced unanswered choice draws nothing
  (no stem without options); the current question keeps its stem while busy.
- Copy text skips a dead question.
- Three DOM tests reproduce 「stem, stem」 and 「dead stem + unavailable」, red then green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017eEAG8HD3mm8gsKXgk8uU8

frontend/src/components/rectification-message-entry.tsx

@@ -27,6 +27,7 @@ import {
 } from "@/lib/rectification-agentic/v9/choice-card";
 import {
   questionIsAnswered,
+  questionIsDeadUnanswered,
   type TurnQuestion,
 } from "@/lib/rectification-agentic/v9/turn-question";
 import { RECTIFICATION_STOPPED_NOTICE } from "@/lib/rectification-surface-state";
@@ -152,7 +153,16 @@ function RectificationMessageEntryView({
   const embeddedCard = question && !unansweredDeadChoice
     ? choiceCardFromQuestion(question, liveQuestion ? liveChoiceCard : null)
     : null;
-  const afterAnswer = question && displayedMessage.state === "settled"
+  // BUG-1135 (D1, supersedes BUG-917's 「stem without options」): a choice
+  // nobody can answer any more draws nothing on its message — only the live
+  // focus prints a stem, so the same stem never shows twice.
+  const replacedQuestion = Boolean(
+    question
+    && unansweredDeadChoice
+    && (questionIsDeadUnanswered(question)
+      || (currentQuestionFocusId !== null && currentQuestionFocusId !== question.focus_id)),
+  );
+  const afterAnswer = question && displayedMessage.state === "settled" && !replacedQuestion
     ? (
       <div className="rectification-message-question">
         <p className="rectification-message-question__prompt">{question.prompt}</p>