feat(merge): 自动合并失败时建最高优先级补救任务来完成合并

decide 端 exec_review accept→merge 冲突失败时,不再只是报错留在闸:
自动建一个 P0 easy 补救任务(operations 写明分支/目标/冲突详情与解冲突步骤),
自治项目会自动领取去解决。幂等:补救任务 id 记到原任务 result.mergeTaskId,
已有未结束补救任务则复用不重复建;结束(done/cancelled)后允许新建。

- model/types: TaskResult 加 mergeTaskId 字段
- mappers/orchestrator: 同步透传/补 null
- store.ensureMergeRemediationTask + store.test 覆盖(P0/easy/ready/operations/幂等/可重建)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/orchestrator.test.ts

@@ -184,6 +184,7 @@ test('成功路径：状态流转 + setResult(四字段) + executor/reviewer/sec
     verdict: 'approve',
     securitySummary: '## 安全审计\nmock 审计通过',
     securityVerdict: 'approve',
+    mergeTaskId: null,
   });
   assert.equal(codeReportSeen, '执行自述：改了 README');   // runner finalText 传给两个复审作执行者自述
   assert.equal(secReportSeen, '执行自述：改了 README');

test/store.test.ts

@@ -208,3 +208,46 @@ test('容器收口：已拆解 Hard 的子任务全 done → 容器自动 done
   assert.equal(s.getTask(root.id).status, 'done');         // 子全 done → 容器自动 done
   s.close();
 });
+
+test('合并失败补救：建最高优先级 easy 任务，且幂等不重复建', () => {
+  const s = freshStore();
+  const p = s.createProject({ name: 'm', repoPath: '/tmp/m-' + Math.random() });
+  // 造一个进入 exec_review、带分支结果的原任务
+  const t = s.createTask({ projectId: p.id, title: '配置面板补 model', complexity: 'easy', priority: 1 });
+  s.setOperations(t.id, 'op');
+  s.transition(t.id, 'queued');
+  s.transition(t.id, 'executing');
+  s.setResult(t.id, {
+    branch: 'maestro/' + t.id, worktree: '/tmp/wt', diffSummary: '', commits: [], prUrl: null,
+    summary: null, verdict: null, securitySummary: null, securityVerdict: null, mergeTaskId: null,
+  });
+  s.transition(t.id, 'exec_review');
+
+  const rem = s.ensureMergeRemediationTask(t.id, {
+    branch: 'maestro/' + t.id, targetBranch: 'main', conflictError: '冲突文件：web/app.js',
+  });
+  assert.equal(rem.complexity, 'easy');
+  assert.equal(rem.priority, 0, '补救任务应为最高优先级 P0');
+  assert.equal(rem.status, 'ready', 'easy 无依赖 → 直达 ready，自治项目可领');
+  assert.match(rem.title, /合并冲突待解决/);
+  assert.match(rem.operations ?? '', /git merge maestro\//, 'operations 应含合并步骤');
+  assert.match(rem.operations ?? '', /web\/app\.js/, 'operations 应含冲突详情');
+  // 幂等标记写回原任务
+  assert.equal(s.getTask(t.id).result?.mergeTaskId, rem.id);
+
+  // 再次调用 → 复用同一补救任务，不新建
+  const again = s.ensureMergeRemediationTask(t.id, {
+    branch: 'maestro/' + t.id, targetBranch: 'main', conflictError: '再次冲突',
+  });
+  assert.equal(again.id, rem.id, '已有未结束补救任务 → 复用');
+  const remCount = s.listTasks(p.id).filter((x) => x.title.includes('合并冲突待解决')).length;
+  assert.equal(remCount, 1, '不应重复建补救任务');
+
+  // 补救任务结束（cancelled）后再调用 → 允许新建
+  s.transition(rem.id, 'cancelled');
+  const fresh = s.ensureMergeRemediationTask(t.id, {
+    branch: 'maestro/' + t.id, targetBranch: 'main', conflictError: '又冲突',
+  });
+  assert.notEqual(fresh.id, rem.id, '旧补救任务已结束 → 建新的');
+  s.close();
+});