修复 load_markets 超时后狂打交易所：失败退避 90 秒，避免反复请求导致封 IP。

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_markets_load_guard_lib.py

@@ -0,0 +1,40 @@
+"""markets load backoff guard."""
+from __future__ import annotations
+
+import unittest
+
+from lib.trade.markets_load_guard_lib import MarketsLoadGuard
+
+
+class TestMarketsLoadGuard(unittest.TestCase):
+    def test_success_sets_loaded(self):
+        g = MarketsLoadGuard(backoff_sec=60.0, label="t")
+        calls = {"n": 0}
+
+        def load():
+            calls["n"] += 1
+
+        g.ensure(load)
+        self.assertTrue(g.loaded)
+        g.ensure(load)
+        self.assertEqual(calls["n"], 1)
+
+    def test_failure_backs_off(self):
+        g = MarketsLoadGuard(backoff_sec=60.0, label="t")
+        calls = {"n": 0}
+
+        def load():
+            calls["n"] += 1
+            raise TimeoutError("boom")
+
+        with self.assertRaises(TimeoutError):
+            g.ensure(load)
+        self.assertFalse(g.loaded)
+        self.assertEqual(calls["n"], 1)
+        with self.assertRaises(RuntimeError):
+            g.ensure(load)
+        self.assertEqual(calls["n"], 1)
+
+
+if __name__ == "__main__":
+    unittest.main()