emrg: start_daemon 超时附加 emrgd.log 尾部真实原因（R124）

emrg/client/daemon_manager.py

@@ -67,6 +67,24 @@ def is_running() -> bool:
     return is_server_running_sync()
 
 
+def _tail_daemon_log(log_path: Path | None = None, max_lines: int = 20) -> str:
+    """Return the tail of ~/.emrg/emrgd.log (best-effort).
+
+    Used when the daemon fails to start within the timeout: stderr is
+    DEVNULL, so the RotatingFileHandler log (~/.emrg/emrgd.log) is the only
+    place the real failure reason survives (rant 2026-08-05T15:54:28 关联项 —
+    config.toml 解析错误等曾只显示 "failed to start within timeout").
+    """
+    try:
+        log_file = log_path or (Path.home() / ".emrg" / "emrgd.log")
+        if not log_file.exists():
+            return "no emrgd.log"
+        lines = log_file.read_text(encoding="utf-8", errors="replace").splitlines()
+        return " | ".join(lines[-max_lines:]) or "empty emrgd.log"
+    except OSError as e:
+        return f"cannot read emrgd.log: {e}"
+
+
 async def start_daemon() -> subprocess.Popen:
     """Start emrgd in the background and wait until it accepts connections."""
     logger.info("starting emrgd daemon...")
@@ -80,7 +98,8 @@ async def start_daemon() -> subprocess.Popen:
         if is_running():
             logger.info("emrgd started (pid=%d)", proc.pid)
             return proc
-    raise RuntimeError("emrgd failed to start within timeout")
+    # R124: 附加 daemon 日志尾部真实原因（stderr 被 DEVNULL 丢弃，日志是唯一线索）
+    raise RuntimeError(f"emrgd failed to start within timeout: {_tail_daemon_log()}")
 
 
 async def check_and_restart_if_stale() -> None:

tests/test_daemon_manager.py

@@ -103,6 +103,46 @@ async def _run():
 
         asyncio.run(_run())
 
+    @patch("emrg.client.daemon_manager.is_running", return_value=False)
+    @patch("emrg.client.daemon_manager.cleanup_server")
+    @patch("emrg.client.daemon_manager.asyncio.create_subprocess_exec",
+           new_callable=AsyncMock)
+    def test_timeout_appends_log_tail(self, mock_spawn, mock_cleanup, mock_is_running):
+        """R124: 超时错误附带 emrgd.log 尾部真实原因（stderr 被 DEVNULL 丢弃）。"""
+        tmp = Path(tempfile.mkdtemp())
+        emrg_dir = tmp / ".emrg"
+        emrg_dir.mkdir()
+        (emrg_dir / "emrgd.log").write_text(
+            "12:00:01 [ERROR] emrg.config: vision = trues 解析失败\n"
+            "12:00:02 [ERROR] emrg.server: config load failed\n",
+            encoding="utf-8",
+        )
+        mock_spawn.return_value = MagicMock(pid=1234)
+
+        async def _run():
+            with pytest.raises(RuntimeError) as exc_info:
+                await daemon_manager.start_daemon()
+            assert "failed to start" in str(exc_info.value)
+            assert "vision = trues" in str(exc_info.value)
+            assert "config load failed" in str(exc_info.value)
+
+        with patch("emrg.client.daemon_manager.Path.home",
+                   return_value=tmp):
+            asyncio.run(_run())
+
+    def test_tail_daemon_log_no_file(self):
+        tmp = Path(tempfile.mkdtemp())
+        result = daemon_manager._tail_daemon_log(tmp / "missing.log")
+        assert result == "no emrgd.log"
+
+    def test_tail_daemon_log_reads_tail(self):
+        tmp = Path(tempfile.mkdtemp())
+        log = tmp / "emrgd.log"
+        log.write_text("\n".join(f"line {i}" for i in range(30)), encoding="utf-8")
+        result = daemon_manager._tail_daemon_log(log, max_lines=5)
+        assert "line 29" in result
+        assert "line 0" not in result  # 只读尾部
+
 
 # ── check_and_restart_if_stale ───────────────────────────────