feat: add low-cardinality observation port

app/adapters/web/metrics.py

@@ -0,0 +1,58 @@
+"""HTTP route/status/latency 指标 ASGI 适配器。"""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+from app.runtime.observability import record_metric
+from starlette.routing import Match
+
+
+class HttpMetricsMiddleware:
+    """按路由模板、方法和状态码记录低基数 HTTP 时延。"""
+
+    def __init__(self, app: Any) -> None:
+        """保存下游 ASGI 应用。"""
+        self._app = app
+
+    async def __call__(self, scope: dict, receive: Any, send: Any) -> None:
+        """只治理 HTTP scope，并在响应开始后读取路由模板。"""
+        if scope.get("type") != "http":
+            await self._app(scope, receive, send)
+            return
+        started_at = time.perf_counter()
+        status = "500"
+
+        async def send_with_metrics(message: dict) -> None:
+            """捕获响应状态并原样转发 ASGI 消息。"""
+            nonlocal status
+            if message.get("type") == "http.response.start":
+                status = str(message.get("status", 500))
+            await send(message)
+
+        try:
+            await self._app(scope, receive, send_with_metrics)
+        finally:
+            route_path = self._resolve_route_template(scope)
+            record_metric(
+                "http.server.duration",
+                time.perf_counter() - started_at,
+                route=route_path,
+                method=str(scope.get("method", "UNKNOWN")),
+                status=status,
+            )
+
+    def _resolve_route_template(self, scope: dict) -> str:
+        """遍历 ASGI wrapper 找到匹配路由模板，绝不回退到具体请求 path。"""
+        route = scope.get("route")
+        if getattr(route, "path", None):
+            return route.path
+        candidate = self._app
+        while candidate is not None:
+            for registered_route in getattr(candidate, "routes", ()):
+                match, _ = registered_route.matches(scope)
+                if match == Match.FULL:
+                    return getattr(registered_route, "path", "unmatched")
+            candidate = getattr(candidate, "app", None)
+        return "unmatched"