feat(observability): /health 不再产生 server span

容器 HEALTHCHECK 每 30 秒探一次、上游也在轮询，这些请求各自是一条孤立
trace，量大且没有信息量——和 worker 空转长轮询同一个问题，把观测后台刷满
的正是它们。

instrument_app 传 excluded_urls，由新增的 RAKUTEN_OTEL_EXCLUDED_URLS 控制
（默认 /health$）。按 search 匹配完整 URL，锚点保证不误伤 /api/health-*；
留空时传 None，回落到 OTel 自己的 OTEL_PYTHON_FASTAPI_EXCLUDED_URLS。

三个服务共用 instrument_app，因此抓取/交易/网关一并生效。

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_telemetry.py

@@ -15,12 +15,15 @@ from __future__ import annotations
 import pytest
 from fastapi import FastAPI
 from opentelemetry import trace
+from opentelemetry.instrumentation import fastapi as otel_fastapi
+from opentelemetry.instrumentation.asgi import OpenTelemetryMiddleware
 from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
 from opentelemetry.instrumentation.httpx import HTTPXClientInstrumentor
 from opentelemetry.sdk.trace import TracerProvider
 from opentelemetry.sdk.trace.export import SimpleSpanProcessor
 from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
 from opentelemetry.trace import StatusCode
+from opentelemetry.util.http import parse_excluded_urls
 
 from app.shared import telemetry
 from app.shared.config import Settings
@@ -70,6 +73,59 @@ def test_instrument_app_works_before_setup_telemetry(monkeypatch):
         FastAPIInstrumentor.uninstrument_app(app)
 
 
+def _otel_middleware(app: FastAPI) -> OpenTelemetryMiddleware:
+    """从构建好的中间件栈里挖出 ASGI 打桩中间件，用于断言它的排除规则"""
+    node = app.build_middleware_stack()
+    while node is not None:
+        if isinstance(node, OpenTelemetryMiddleware):
+            return node
+        node = getattr(node, "app", None)
+    raise AssertionError("中间件栈里没有 OpenTelemetryMiddleware")
+
+
+def test_health_excluded_from_server_spans(monkeypatch):
+    """/health 不产生 server span，其它路径照常
+
+    容器 HEALTHCHECK 每 30 秒探一次、上游也在轮询，这些请求各自是一条孤立 trace，
+    量大且没有信息量。排除规则按 search 匹配完整 URL，所以要钉住两件事：/health
+    真的被挡掉，且 `$` 锚点没有顺手把 /api/* 一起挡掉。
+    """
+    monkeypatch.setattr(
+        telemetry, "get_settings", lambda: Settings(_env_file=None, otel_enabled=True)
+    )
+    app = FastAPI()
+    try:
+        telemetry.instrument_app(app)
+        excluded = _otel_middleware(app).excluded_urls
+        assert excluded.url_disabled("http://127.0.0.1:31108/health")
+        assert not excluded.url_disabled("http://127.0.0.1:31108/api/cart/add")
+        # 前缀匹配会误伤的反例：锚点保证只有 /health 本身被排除
+        assert not excluded.url_disabled("http://127.0.0.1:31108/api/health-detail")
+    finally:
+        FastAPIInstrumentor.uninstrument_app(app)
+
+
+def test_excluded_urls_empty_falls_back_to_env(monkeypatch):
+    """配置留空时传 None，让 OTel 回落到它自己的环境变量而不是排除空字符串"""
+    monkeypatch.setattr(
+        telemetry,
+        "get_settings",
+        lambda: Settings(_env_file=None, otel_enabled=True, otel_excluded_urls="  "),
+    )
+    # OTel 那份环境变量在模块导入时就解析成常量了，setenv 已经晚了，只能直接替常量
+    monkeypatch.setattr(
+        otel_fastapi, "_excluded_urls_from_env", parse_excluded_urls("/metrics")
+    )
+    app = FastAPI()
+    try:
+        telemetry.instrument_app(app)
+        excluded = _otel_middleware(app).excluded_urls
+        assert excluded.url_disabled("http://127.0.0.1:31108/metrics")
+        assert not excluded.url_disabled("http://127.0.0.1:31108/health")
+    finally:
+        FastAPIInstrumentor.uninstrument_app(app)
+
+
 def test_instrument_app_skipped_when_otel_disabled(monkeypatch):
     """otel 关闭时不装中间件，省掉一层用不上的开销"""
     monkeypatch.setattr(