test(client): filter known Starlette portal deprecation

s2s-client/CHANGELOG.md

@@ -9,6 +9,8 @@ the implementation at the recorded date; current operating instructions live in
 
 ### Changed
 
+- Filter the specific Starlette TestClient / AnyIO `BlockingPortal` deprecation
+  in pytest while retaining the runtime versions used for compatibility captures.
 - Added a uv-managed Python 3.12 environment and Ruff, mypy, and pytest quality
   checks, all contained in `s2s-client/`. Startup and Docker use the committed
   lockfile. Split the FastAPI service into configuration, route, provider,

s2s-client/pyproject.toml

@@ -67,3 +67,9 @@ warn_untyped_fields = true
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 pythonpath = ["."]
+# Starlette 0.41.3 uses an alias deprecated by AnyIO 4.15. Keep the runtime
+# versions used for compatibility captures; remove this test-only exception
+# when upgrading Starlette. Upstream: https://github.com/Kludex/starlette/issues/3497
+filterwarnings = [
+  'ignore:^The anyio\.abc\.BlockingPortal alias is deprecated, use anyio\.from_thread\.BlockingPortal instead\.$:DeprecationWarning:^starlette\.testclient$',
+]