diff --git a/emrg/client/daemon_manager.py b/emrg/client/daemon_manager.py
index 7dcfa642..4e6709fe 100644
--- a/emrg/client/daemon_manager.py
+++ b/emrg/client/daemon_manager.py
@@ -80,7 +80,22 @@ 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: 超时后读取 emrgd.log 尾部打印真实失败原因（rant 2026-08-05T15:54:28 关联：
+    # config.toml 解析错误时 CLI 只显示 'failed to start within timeout'，吞掉真实报错）
+    tail = _read_log_tail(Path.home() / ".emrg" / "emrgd.log", lines=15)
+    detail = f"\n  emrgd.log 尾部:\n{tail}" if tail else ""
+    raise RuntimeError(f"emrgd failed to start within timeout{detail}")
+
+
+def _read_log_tail(path: Path, lines: int = 15) -> str:
+    """Return the last `lines` of a log file (empty string on any error)."""
+    try:
+        if not path.exists():
+            return ""
+        data = path.read_text(encoding="utf-8", errors="replace")
+        return "\n".join(data.rstrip().splitlines()[-lines:])
+    except OSError:
+        return ""
 
 
 async def check_and_restart_if_stale() -> None:
diff --git a/tests/test_daemon_manager.py b/tests/test_daemon_manager.py
index cfc625d3..10eec195 100644
--- a/tests/test_daemon_manager.py
+++ b/tests/test_daemon_manager.py
@@ -287,3 +287,26 @@ def test_close_calls_ws_close(self):
         conn = self._conn()
         asyncio.run(conn.close())
         assert conn._ws.closed is True
+
+class TestReadLogTail:
+    """_read_log_tail — daemon start-timeout diagnostics (R124)."""
+
+    def test_tail_last_lines(self, tmp_path):
+        p = tmp_path / "emrgd.log"
+        p.write_text("\n".join(f"line{i}" for i in range(1, 31)), encoding="utf-8")
+        out = daemon_manager._read_log_tail(p, lines=5)
+        assert out == "line26\nline27\nline28\nline29\nline30"
+
+    def test_missing_file_returns_empty(self, tmp_path):
+        assert daemon_manager._read_log_tail(tmp_path / "nope.log") == ""
+
+    def test_shorter_than_lines_returns_all(self, tmp_path):
+        p = tmp_path / "emrgd.log"
+        p.write_text("a\nb", encoding="utf-8")
+        assert daemon_manager._read_log_tail(p, lines=10) == "a\nb"
+
+    def test_invalid_utf8_replaced(self, tmp_path):
+        p = tmp_path / "emrgd.log"
+        p.write_bytes(b"ok\n\xff\xfebad\nend")
+        out = daemon_manager._read_log_tail(p, lines=5)
+        assert "end" in out and "\ufffd" in out