feat(HEL-382): 搭建 datahub 底座和盘后正式数据链路

新增独立 xiaobai-datahub 服务（SQLite WAL、Tushare 盘后发布、/v1 契约和管理后台），不改现站页面与数据链路。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

xiaobai-datahub/tests/test_governance.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import unittest
+
+from datahub.governance.circuit import CircuitBreaker
+from datahub.governance.ratelimit import TokenBucket
+from datahub.governance.retry import RetryError, retry_call
+
+
+class FakeClock:
+    def __init__(self) -> None:
+        self.value = 0.0
+
+    def __call__(self) -> float:
+        return self.value
+
+
+class GovernanceTests(unittest.TestCase):
+    def test_token_bucket_caps_burst_at_capacity(self) -> None:
+        clock = FakeClock()
+        bucket = TokenBucket(rate_per_minute=300, capacity=300, clock=clock)
+        ok = 0
+        for _ in range(400):
+            if bucket.acquire(block=False):
+                ok += 1
+        self.assertEqual(ok, 300)
+        clock.value = 60
+        self.assertTrue(bucket.acquire(block=False))
+
+    def test_circuit_opens_after_five_failures_and_half_opens(self) -> None:
+        clock = FakeClock()
+        breaker = CircuitBreaker(clock=clock, open_seconds=120)
+        for _ in range(5):
+            breaker.record_failure("boom")
+        self.assertEqual(breaker.snapshot().state, "open")
+        self.assertFalse(breaker.allow())
+        clock.value = 120
+        self.assertEqual(breaker.snapshot().state, "half_open")
+        self.assertTrue(breaker.allow())
+        breaker.record_success()
+        self.assertEqual(breaker.snapshot().state, "closed")
+
+    def test_retry_exhausts(self) -> None:
+        calls = {"n": 0}
+
+        def fail():
+            calls["n"] += 1
+            raise RuntimeError("no")
+
+        with self.assertRaises(RetryError):
+            retry_call(fail, attempts=3, sleeper=lambda _d: None)
+        self.assertEqual(calls["n"], 3)
+
+
+if __name__ == "__main__":
+    unittest.main()