Docker default repo + keep stderr in worker error_text

Two live-test findings in one fix:
1. DockerExecutor has no repo fallback: when a project has no
repo_url, worker leaves task['repo'] unset and the container
host.py dispatch fails instantly with 'missing --repo' because
host-config-docker.json had no repo field either. Add the host
test-repo as the config default; projects with repo_url still
override it via worker's explicit --repo.
2. Worker discarded stderr from the final error_text, so every
container/host crash surfaced only as the generic 'host
execution failed' and was undebuggable from the task record.
When stdout is empty, error_text now keeps the stderr tail
(last 1000 chars, where the real error line lives).

cloud/tests/test_fallback_retry.py

@@ -324,6 +324,28 @@ class FallbackRetryTestCase(unittest.TestCase):
         self.assertEqual(len(self.calls), 1)
         self.assertEqual(result["events"], [])
 
+    def test_crash_without_code_error_text_keeps_stderr(self):
+        # stdout 为空、stderr 有真实报错时，最终 error_text 必须
+        # 留住 stderr，不能被通用的 host execution failed 盖掉
+        # （主机实测：缺 repo 的 1 秒失败曾因此完全无法排障）。
+        def fake(cmd):
+            return SimpleNamespace(
+                returncode=1, stdout="",
+                stderr="Traceback (most recent call last):\n"
+                       "RuntimeError: 缺少 --repo，也没有在 host-config.json 里配 repo")
+
+        _insert_task(self.db_path, "A")
+        worker = self._worker(
+            runner=self._recording(fake),
+            model="gpt-6.1-sol",
+            fallback_models=["gpt-6-sol"],
+            max_retries=0)
+        result = worker.run_one()
+        self.assertEqual(result["status"], "failed")
+        row, cost, audits = _execution(self.db_path, "A")
+        self.assertIn("缺少 --repo", row[0])
+        self.assertEqual(result["events"], [])
+
 
 if __name__ == "__main__":
     unittest.main()

cloud/worker.py

@@ -905,6 +905,13 @@ class Worker:
             parsed = None
         if isinstance(parsed, dict) and parsed.get("text"):
             return str(parsed["text"])
+        # host.py 崩溃时 stdout 常为空、真正的报错在 stderr（例如
+        # “缺少 --repo”、Read-only file system）；只用 stdout 时
+        # 最终错误会被写成通用的 host execution failed，排障无从
+        # 下手，所以 stdout 为空时取 stderr 尾部（实际报错行在尾）。
+        stderr = (result or {}).get("stderr", "") or ""
+        if not stdout.strip() and stderr.strip():
+            return stderr.strip()[-1000:]
         if token is not None:
             return "host_status=%s" % token
         return stdout.strip() or "host execution failed"
@@ -1124,7 +1131,10 @@ class Worker:
                             fallback_model, second_error))
             else:
                 if error is None:
-                    error = stdout.strip() or "host execution failed"
+                    stderr = (result or {}).get("stderr", "") or ""
+                    error = stdout.strip() or \
+                        (stderr.strip()[-1000:] if stderr.strip() else "") \
+                        or "host execution failed"
                 if retry_count:
                     error = "[retries=%d] %s" % (retry_count, error)
                 # 未配 fallback_models 时的老行为：只记事件、不重试。

host-config-docker.json

@@ -1 +1 @@
-{"_note":"Docker 执行器专用配置（容器内路径，绝不是宿主路径）：state 必须用相对路径 work/host-state.json——相对配置文件所在目录 /app 解析，得到 /app/work/host-state.json，经额外挂载落到宿主 /opt/codex-app-server/work/host-state.json，属主是 codexsvc（uid 1003，与容器 --user 1003:1004 一致），容器可写。绝不能用默认的 /app/host-state.json（/app 是只读挂载，锁一开就报 Read-only file system），也绝不能用 /work/host-state.json（/work 挂载的宿主目录由 docker 自动创建、属主 root，容器用户写不进去，同样 1 秒内失败）。此文件曾因 deploy 清理被删过（不在仓库里），导致 Docker 派发静默全灭，所以它必须进仓库、随部署一起发。sandbox 用 danger-full-access：主机内核禁止不可信 user namespace，Docker + 内层 bwrap 双重沙箱不可行，生产隔离层就是 Docker 本身。API key 绝不放这里，只走环境变量。","approval":"deny","approval_policy":"never","effort":"low","model":"gpt-6.1-sol","sandbox":"danger-full-access","state":"work/host-state.json"}
+{"_note": "Docker 执行器专用配置（容器内路径，绝不是宿主路径）：state 必须用相对路径 work/host-state.json——相对配置文件所在目录 /app 解析，得到 /app/work/host-state.json，经额外挂载落到宿主 /opt/codex-app-server/work/host-state.json，属主是 codexsvc（uid 1003，与容器 --user 1003:1004 一致），容器可写。绝不能用默认的 /app/host-state.json（/app 是只读挂载，锁一开就报 Read-only file system），也绝不能用 /work/host-state.json（/work 挂载的宿主目录由 docker 自动创建、属主 root，容器用户写不进去，同样 1 秒内失败）。此文件曾因 deploy 清理被删过（不在仓库里），导致 Docker 派发静默全灭，所以它必须进仓库、随部署一起发。sandbox 用 danger-full-access：主机内核禁止不可信 user namespace，Docker + 内层 bwrap 双重沙箱不可行，生产隔离层就是 Docker 本身。API key 绝不放这里，只走环境变量。 默认仓库是宿主测试仓库：没有 repo_url 的项目走它；有 repo_url 的项目 worker 会把解析出的检出经 --repo 传进去，覆盖它。", "approval": "deny", "approval_policy": "never", "effort": "low", "model": "gpt-6.1-sol", "sandbox": "danger-full-access", "state": "work/host-state.json", "repo": "/var/lib/codex-app-server/test-repo"}