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/datahub/governance/lkg.py

@@ -0,0 +1,84 @@
+from __future__ import annotations
+
+import json
+from typing import Any
+
+from datahub.db import HubDB
+from datahub.timeutil import isoformat, now_shanghai
+
+
+class LastKnownGood:
+    def __init__(self, db: HubDB) -> None:
+        self.db = db
+
+    def store(self, cache_key: str, payload: Any, source: str) -> None:
+        self.db.execute(
+            """
+            INSERT INTO last_known_good(cache_key, payload, source, stored_at)
+            VALUES (?, ?, ?, ?)
+            ON CONFLICT(cache_key) DO UPDATE SET
+              payload=excluded.payload, source=excluded.source, stored_at=excluded.stored_at
+            """,
+            (cache_key, json.dumps(payload, ensure_ascii=False), source, isoformat()),
+        )
+
+    def load(self, cache_key: str) -> dict[str, Any] | None:
+        row = self.db.fetchone("SELECT * FROM last_known_good WHERE cache_key = ?", (cache_key,))
+        if not row:
+            return None
+        return {
+            "payload": json.loads(row["payload"]),
+            "source": row["source"],
+            "stored_at": row["stored_at"],
+        }
+
+    def put_rt(self, cache_key: str, payload: Any, source: str, ttl_seconds: int) -> None:
+        now = now_shanghai()
+        expires = isoformat(now.replace(microsecond=0))
+        # expires_at stored as iso; compute by adding ttl via timestamp
+        from datetime import timedelta
+
+        self.db.execute(
+            """
+            INSERT INTO rt_cache(cache_key, payload, source, stored_at, expires_at)
+            VALUES (?, ?, ?, ?, ?)
+            ON CONFLICT(cache_key) DO UPDATE SET
+              payload=excluded.payload, source=excluded.source,
+              stored_at=excluded.stored_at, expires_at=excluded.expires_at
+            """,
+            (
+                cache_key,
+                json.dumps(payload, ensure_ascii=False),
+                source,
+                isoformat(now),
+                isoformat(now + timedelta(seconds=ttl_seconds)),
+            ),
+        )
+        self.store(cache_key, payload, source)
+
+    def get_rt(self, cache_key: str, max_stale_seconds: int | None = None) -> dict[str, Any] | None:
+        row = self.db.fetchone("SELECT * FROM rt_cache WHERE cache_key = ?", (cache_key,))
+        if not row:
+            lkg = self.load(cache_key)
+            if not lkg:
+                return None
+            return {**lkg, "stale": True}
+        stored_at = row["stored_at"]
+        expired = row["expires_at"] < isoformat()
+        result = {
+            "payload": json.loads(row["payload"]),
+            "source": row["source"],
+            "stored_at": stored_at,
+            "stale": expired,
+        }
+        if expired and max_stale_seconds is not None:
+            from datetime import datetime
+
+            try:
+                stored = datetime.fromisoformat(stored_at)
+                age = (now_shanghai() - stored).total_seconds()
+            except ValueError:
+                age = max_stale_seconds + 1
+            if age > max_stale_seconds:
+                return None
+        return result