HEL-543 返工: 补充 observability 运行时可关闭开关 (DATAHUB_OBSERVABILITY)

总工复核 🔴：安全边界要求新增观测功能必须可关闭、关闭后现有功能完全照旧，
但此前实现没有任何运行时开关。修复：

- settings.py: 新增 Settings.observability_enabled 字段，沿用既有
  DATAHUB_SCHEDULER 的环境变量模式，读取 DATAHUB_OBSERVABILITY
  (0/false/off 关闭，默认开启)。
- hub.py: Hub.__init__ 把 settings.observability_enabled 挂到
  self.db 上，让 pipeline/realtime_serve/steward/admin_api 已经
  在传的 db 参数直接带上开关，零额外改造。
- observability.py: 新增 is_enabled(db)，缺失该属性时默认按启用处理
  (向后兼容裸 HubDB 用例/测试)。关闭时 observe() 变成纯
  透传（不计时、不分类、不碰数据库)，record_call() 直接 no-op。
- admin_api.py: 4 个新只读端点关闭时返回明确的
  {"enabled": false, ...空结构} 而不是静默返回旧数据。
- 新增 10 个测试：开关默认值/环境变量解析、关闭后 observe() 的透传语义
  (含异常原样重新抛出)、关闭后 record_call() 零写入、关闭后重新开启恢复
  记录、4 个 admin 端点在关闭态的响应结构。

全量测试 183/183 通过（新增 10 个，含此前 173 个零回归）。

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

xiaobai-datahub/datahub/admin_api.py

@@ -7,6 +7,7 @@ from datahub.adapters import RESERVED
 from datahub.auth import AuthService
 from datahub.db import HubDB
 from datahub import lineage as lineage_module
+from datahub import observability
 from datahub.pipeline import OFFICIAL_DATASETS, STOCKS_DATASET, Pipeline
 from datahub.scheduler import Scheduler
 from datahub.serving import ApiError
@@ -114,6 +115,8 @@ class AdminAPI:
     # static registries in source_catalog.py / lineage.py.
     # ------------------------------------------------------------------
     def providers_status(self, provider: str = "", limit: int = 50) -> dict[str, Any]:
+        if not observability.is_enabled(self.db):
+            return {"enabled": False, "health": [], "recent_calls": []}
         limit = max(1, min(int(limit or 50), 200))
         health_sql = "SELECT * FROM provider_health"
         params: tuple[Any, ...] = ()
@@ -127,19 +130,30 @@ class AdminAPI:
             calls_sql += " WHERE provider = ?"
         calls_sql += " ORDER BY id DESC LIMIT ?"
         recent = self.db.fetchall(calls_sql, (*params, limit))
-        return {"health": health, "recent_calls": recent}
+        return {"enabled": True, "health": health, "recent_calls": recent}
 
     def source_catalog(self) -> dict[str, Any]:
-        return {"items": source_catalog.snapshot(self.db, self.auth)}
+        if not observability.is_enabled(self.db):
+            return {"enabled": False, "items": []}
+        return {"enabled": True, "items": source_catalog.snapshot(self.db, self.auth)}
 
     def lineage(self, trade_date: str = "") -> dict[str, Any]:
         day = yyyymmdd(trade_date) if trade_date else yyyymmdd(now_shanghai())
-        return {"trade_date": day, "items": lineage_module.snapshot(self.db, day)}
+        if not observability.is_enabled(self.db):
+            return {"enabled": False, "trade_date": day, "items": []}
+        return {"enabled": True, "trade_date": day, "items": lineage_module.snapshot(self.db, day)}
 
     def lineage_affected(self, provider: str = "", interface: str = "") -> dict[str, Any]:
         if not provider:
             raise ApiError("INVALID_ARGUMENT", "provider is required")
-        return {"provider": provider, "interface": interface, "items": lineage_module.affected(self.db, provider, interface)}
+        if not observability.is_enabled(self.db):
+            return {"enabled": False, "provider": provider, "interface": interface, "items": []}
+        return {
+            "enabled": True,
+            "provider": provider,
+            "interface": interface,
+            "items": lineage_module.affected(self.db, provider, interface),
+        }
 
     def jobs(self) -> dict[str, Any]:
         runs = self.db.fetchall("SELECT * FROM job_runs ORDER BY id DESC LIMIT 100")

xiaobai-datahub/datahub/hub.py

@@ -24,6 +24,12 @@ class Hub:
             raise SystemExit("DATAHUB_ENCRYPTION_KEY 未配置")
         self.settings = settings
         self.db = HubDB(settings.db_path)
+        # HEL-543: carry the observability kill switch on the db handle so
+        # every call site that already threads `db` through (pipeline,
+        # realtime_serve, steward, admin_api) picks it up for free with no
+        # extra plumbing. Missing this attribute (e.g. a bare HubDB built
+        # directly in tests) defaults to enabled — see observability.is_enabled.
+        self.db.observability_enabled = settings.observability_enabled
         self.vault = SecretVault(settings.encryption_key)
         self.auth = AuthService(self.db, self.vault, settings.api_token, settings.admin_password)
         token = settings.tushare_token or self.auth.load_credential("tushare_token")

xiaobai-datahub/datahub/observability.py

@@ -81,6 +81,21 @@ def _logger():
     return get_logger()
 
 
+def is_enabled(db: Any) -> bool:
+    """Runtime kill switch (``Settings.observability_enabled`` /
+    ``DATAHUB_OBSERVABILITY``, wired onto the db handle in ``Hub.__init__``).
+
+    Defaults to enabled when the attribute is absent — e.g. a bare ``HubDB``
+    built directly in a test, or any call site that predates HEL-543 — so
+    this can never accidentally disable an existing deployment. Never
+    raises.
+    """
+    try:
+        return bool(getattr(db, "observability_enabled", True))
+    except Exception:  # pragma: no cover - defensive, must never raise
+        return True
+
+
 def classify_error(message: str) -> tuple[str, str]:
     """Best-effort, side-reading classification of an exception message.
 
@@ -171,7 +186,7 @@ def record_call(
 ) -> None:
     """Fail-open recorder. Never raises; a write failure here must never be
     able to take down a real, otherwise-successful data path."""
-    if db is None:
+    if db is None or not is_enabled(db):
         return
     try:
         now = isoformat(now_shanghai())
@@ -282,8 +297,12 @@ def observe(
     Returns exactly what ``fn()`` returns and re-raises exactly what
     ``fn()`` raises. ``db`` may be ``None`` (e.g. in call sites that are not
     wired to a database yet); in that case this is a transparent passthrough
-    with no recording at all.
+    with no recording at all. Same when the ``DATAHUB_OBSERVABILITY`` kill
+    switch is off (see ``is_enabled``): this becomes ``return fn()`` with no
+    timing, no classification, and no db access whatsoever.
     """
+    if db is not None and not is_enabled(db):
+        return fn()
     started = time.perf_counter()
     try:
         result = fn()

xiaobai-datahub/datahub/settings.py

@@ -33,6 +33,11 @@ class Settings:
     quality: dict[str, Any] = field(default_factory=dict)
     log_level: str = "INFO"
     scheduler_enabled: bool = True
+    # HEL-543 kill switch: off disables the provider_call_log/provider_health
+    # side channel entirely (observe()/record_call() become no-ops and the
+    # new read-only admin endpoints report {"enabled": false}). Default on;
+    # existing routing/fetch/publish behavior is identical either way.
+    observability_enabled: bool = True
 
     @property
     def tushare_rate_per_minute(self) -> int:
@@ -126,4 +131,5 @@ def load_settings(
         quality=_load_quality(quality_path),
         log_level=environ.get("DATAHUB_LOG_LEVEL") or "INFO",
         scheduler_enabled=str(environ.get("DATAHUB_SCHEDULER") or "1") not in {"0", "false", "False"},
+        observability_enabled=str(environ.get("DATAHUB_OBSERVABILITY") or "1") not in {"0", "false", "False", "off", "OFF"},
     )