分页切片开头的前导条目并进后面那个回合

- buildDirectChatTurns 先攒住第一个用户条目之前的过程条目，交给后面那个回合
- 不再渲染没有用户气泡的孤儿回合；整份历史都没有用户条目时仍保留一个回合
- directTurnPresentation 单测补一条分页切片从半截回合开头的情形

apps/ai-game-creator-shell/src/features/project-workspace/directTurnPresentation.ts

@@ -149,17 +149,30 @@ export function buildDirectChatTurns({
 }): DirectChatTurn[] {
   const turns: DirectChatTurnEntries[] = [];
   let current: DirectChatTurnEntries | null = null;
+  // 分页切片的开头可能落在半截回合里（那一条用户条目还在更早的一屏）：这些前导条目先攒着，
+  // 交给后面第一个用户条目开的回合，避免渲染出一个没有用户气泡的孤儿回合。
+  const leadingEntries: DirectChatEntry[] = [];
   for (const entry of entries) {
     if (entry.kind === 'message' && entry.role === 'user') {
       current = newTurn(entry.itemId);
       turns.push(current);
+      if (leadingEntries.length > 0) {
+        current.entries.push(...leadingEntries);
+        leadingEntries.length = 0;
+      }
     }
     if (!current) {
-      current = newTurn(`history:${turns.length}`);
-      turns.push(current);
+      leadingEntries.push(entry);
+      continue;
     }
     current.entries.push(entry);
   }
+  if (!current && leadingEntries.length > 0) {
+    // 整份历史都没有用户条目：仍然保留一个回合承载正文。
+    current = newTurn(`history:${turns.length}`);
+    current.entries.push(...leadingEntries);
+    turns.push(current);
+  }
 
   const entryIds = new Set(entries.map((entry) => entry.itemId));
   localMessages.forEach((message, index) => {

apps/ai-game-creator-shell/tests/directTurnPresentation.test.ts

@@ -202,6 +202,27 @@ describe('DirectProject 聊天分区', () => {
     expect(turns[0]?.finals[0]).toMatchObject({ text: '只有回复' });
   });
 
+  it('分页切片开头落在半截回合里时并进后面那个回合，不生成没有用户气泡的孤儿回合', () => {
+    // 更早的一屏把上一条用户条目切在外面：这三条前导条目属于上一轮，但不能自成回合。
+    const turns = buildDirectChatTurns({
+      entries: [
+        reasoningEntry('r-prev'),
+        toolEntry('t-prev'),
+        assistantEntry('a-prev', '上一轮的答复', 1_800_000_000_900),
+        userEntry('u2', 1_800_000_010_000),
+        assistantEntry('a2', '这一轮的答复', 1_800_000_011_000),
+      ],
+    });
+    expect(turns.map((turn) => turn.key)).toEqual(['u2']);
+    expect(turns[0]?.users.map((block) => block.key)).toEqual(['u2:u2']);
+    expect(turns[0]?.process.map((block) => block.key)).toEqual([
+      'u2:r-prev',
+      'u2:t-prev',
+      'u2:a-prev',
+    ]);
+    expect(turns[0]?.finals.map((block) => block.key)).toEqual(['u2:a2']);
+  });
+
   it('条目转消息只保留用户 / 助手正文，并按身份去重', () => {
     const messages = directChatEntriesToMessages([
       userEntry('u1'),